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 $41.57   12.794%   $46.8885   $46.89   $46.90   $46.90  
  Purchase #2 $243.27   8.584%   $264.1523   $264.15   $264.15   $264.20  
  Purchase #3 $119.94   8.824%   $130.5235   $130.52   $130.50   $130.50  
  Purchase #4 $190.99   3.251%   $197.1991   $197.20   $197.20   $197.20  
  Purchase #5 $134.28   11.286%   $149.4348   $149.43   $149.45   $149.40  
  Purchase #6 $87.51   10.403%   $96.6137   $96.61   $96.60   $96.60  
  Purchase #7 $173.84   3.192%   $179.389   $179.39   $179.40   $179.40  
  7 purchase totals = $991.40       $1,064.2009   $1,064.19   $1,064.20   $1,064.20