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 $88.40   9.343%   $96.6592   $96.66   $96.65   $96.70  
  Purchase #2 $216.88   8.512%   $235.3408   $235.34   $235.35   $235.30  
  Purchase #3 $176.79   13.807%   $201.1994   $201.20   $201.20   $201.20  
  Purchase #4 $6.59   11.261%   $7.3321   $7.33   $7.35   $7.30  
  Purchase #5 $51.59   12.711%   $58.1476   $58.15   $58.15   $58.10  
  Purchase #6 $180.87   4.622%   $189.2298   $189.23   $189.25   $189.20  
  Purchase #7 $125.38   10.536%   $138.59   $138.59   $138.60   $138.60  
  7 purchase totals = $846.50       $926.4989   $926.50   $926.55   $926.40