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 $58.74   8.180%   $63.5449   $63.54   $63.55   $63.50  
  Purchase #2 $237.51   6.541%   $253.0455   $253.05   $253.05   $253.00  
  Purchase #3 $201.50   12.156%   $225.9943   $225.99   $226.00   $226.00  
  Purchase #4 $184.97   9.162%   $201.917   $201.92   $201.90   $201.90  
  Purchase #5 $105.73   5.336%   $111.3718   $111.37   $111.35   $111.40  
  Purchase #6 $41.85   12.183%   $46.9486   $46.95   $46.95   $46.90  
  Purchase #7 $61.58   7.290%   $66.0692   $66.07   $66.05   $66.10  
  7 purchase totals = $891.88       $968.8913   $968.89   $968.85   $968.80