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 $156.56   13.787%   $178.1449   $178.14   $178.15   $178.10  
  Purchase #2 $218.98   9.566%   $239.9276   $239.93   $239.95   $239.90  
  Purchase #3 $56.60   8.863%   $61.6165   $61.62   $61.60   $61.60  
  Purchase #4 $34.30   11.752%   $38.3309   $38.33   $38.35   $38.30  
  Purchase #5 $158.74   9.406%   $173.6711   $173.67   $173.65   $173.70  
  Purchase #6 $94.42   3.738%   $97.9494   $97.95   $97.95   $97.90  
  Purchase #7 $216.31   7.754%   $233.0827   $233.08   $233.10   $233.10  
  7 purchase totals = $935.91       $1,022.7231   $1,022.72   $1,022.75   $1,022.60