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 $159.47   13.777%   $181.4402   $181.44   $181.45   $181.40  
  Purchase #2 $66.97   9.756%   $73.5036   $73.50   $73.50   $73.50  
  Purchase #3 $58.62   6.117%   $62.2058   $62.21   $62.20   $62.20  
  Purchase #4 $223.47   5.218%   $235.1307   $235.13   $235.15   $235.10  
  Purchase #5 $192.71   5.794%   $203.8756   $203.88   $203.90   $203.90  
  Purchase #6 $187.52   13.142%   $212.1639   $212.16   $212.15   $212.20  
  Purchase #7 $44.41   3.621%   $46.0181   $46.02   $46.00   $46.00  
  7 purchase totals = $933.17       $1,014.3379   $1,014.34   $1,014.35   $1,014.30