Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $158.68   13.133%   $179.5194   $179.52   $179.50   $179.50  
  Purchase #2 $228.56   7.451%   $245.59   $245.59   $245.60   $245.60  
  Purchase #3 $167.92   3.117%   $173.1541   $173.15   $173.15   $173.20  
  Purchase #4 $144.74   10.701%   $160.2286   $160.23   $160.25   $160.20  
  Purchase #5 $167.95   10.162%   $185.0171   $185.02   $185.00   $185.00  
  Purchase #6 $173.65   4.340%   $181.1864   $181.19   $181.20   $181.20  
  Purchase #7 $91.69   11.147%   $101.9107   $101.91   $101.90   $101.90  
  7 purchase totals = $1,133.19       $1,226.6063   $1,226.61   $1,226.60   $1,226.60