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 $116.71   4.834%   $122.3518   $122.35   $122.35   $122.40  
  Purchase #2 $160.55   4.625%   $167.9754   $167.98   $168.00   $168.00  
  Purchase #3 $59.92   11.441%   $66.7754   $66.78   $66.80   $66.80  
  Purchase #4 $243.62   6.717%   $259.984   $259.98   $260.00   $260.00  
  Purchase #5 $140.80   11.592%   $157.1215   $157.12   $157.10   $157.10  
  Purchase #6 $58.58   13.596%   $66.5445   $66.54   $66.55   $66.50  
  Purchase #7 $135.84   7.343%   $145.8147   $145.81   $145.80   $145.80  
  7 purchase totals = $916.02       $986.5673   $986.56   $986.60   $986.60