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 $66.64   11.817%   $74.5148   $74.51   $74.50   $74.50  
  Purchase #2 $232.36   12.166%   $260.6289   $260.63   $260.65   $260.60  
  Purchase #3 $19.75   13.203%   $22.3576   $22.36   $22.35   $22.40  
  Purchase #4 $158.50   5.467%   $167.1652   $167.17   $167.15   $167.20  
  Purchase #5 $73.93   7.744%   $79.6551   $79.66   $79.65   $79.70  
  Purchase #6 $103.46   7.475%   $111.1936   $111.19   $111.20   $111.20  
  Purchase #7 $230.25   6.539%   $245.306   $245.31   $245.30   $245.30  
  7 purchase totals = $884.89       $960.8212   $960.83   $960.80   $960.90