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 $68.32   11.869%   $76.4289   $76.43   $76.45   $76.40  
  Purchase #2 $87.61   5.520%   $92.4461   $92.45   $92.45   $92.40  
  Purchase #3 $170.46   6.696%   $181.874   $181.87   $181.85   $181.90  
  Purchase #4 $227.25   4.748%   $238.0398   $238.04   $238.05   $238.00  
  Purchase #5 $81.63   11.570%   $91.0746   $91.07   $91.05   $91.10  
  Purchase #6 $199.84   11.609%   $223.0394   $223.04   $223.05   $223.00  
  Purchase #7 $35.95   9.794%   $39.4709   $39.47   $39.45   $39.50  
  7 purchase totals = $871.06       $942.3737   $942.37   $942.35   $942.30