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 $56.62   9.411%   $61.9485   $61.95   $61.95   $61.90  
  Purchase #2 $182.76   10.316%   $201.6135   $201.61   $201.60   $201.60  
  Purchase #3 $186.53   10.235%   $205.6213   $205.62   $205.60   $205.60  
  Purchase #4 $109.30   10.725%   $121.0224   $121.02   $121.00   $121.00  
  Purchase #5 $108.75   7.287%   $116.6746   $116.67   $116.65   $116.70  
  Purchase #6 $100.74   12.459%   $113.2912   $113.29   $113.30   $113.30  
  Purchase #7 $27.79   11.772%   $31.0614   $31.06   $31.05   $31.10  
  7 purchase totals = $772.49       $851.2329   $851.22   $851.15   $851.20