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 $187.53   8.861%   $204.147   $204.15   $204.15   $204.10  
  Purchase #2 $69.51   13.509%   $78.9001   $78.90   $78.90   $78.90  
  Purchase #3 $169.78   7.393%   $182.3318   $182.33   $182.35   $182.30  
  Purchase #4 $97.56   5.604%   $103.0273   $103.03   $103.05   $103.00  
  Purchase #5 $210.54   11.608%   $234.9795   $234.98   $235.00   $235.00  
  Purchase #6 $178.53   4.261%   $186.1372   $186.14   $186.15   $186.10  
  Purchase #7 $143.29   7.642%   $154.2402   $154.24   $154.25   $154.20  
  7 purchase totals = $1,056.74       $1,143.7631   $1,143.77   $1,143.85   $1,143.60