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 $165.47   11.601%   $184.6662   $184.67   $184.65   $184.70  
  Purchase #2 $185.66   5.419%   $195.7209   $195.72   $195.70   $195.70  
  Purchase #3 $130.27   10.571%   $144.0408   $144.04   $144.05   $144.00  
  Purchase #4 $235.36   12.727%   $265.3143   $265.31   $265.30   $265.30  
  Purchase #5 $168.84   7.316%   $181.1923   $181.19   $181.20   $181.20  
  Purchase #6 $162.27   10.857%   $179.8877   $179.89   $179.90   $179.90  
  Purchase #7 $9.30   4.321%   $9.7019   $9.70   $9.70   $9.70  
  7 purchase totals = $1,057.17       $1,160.5241   $1,160.52   $1,160.50   $1,160.50