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 $93.50   3.494%   $96.7669   $96.77   $96.75   $96.80  
  Purchase #2 $80.80   4.390%   $84.3471   $84.35   $84.35   $84.30  
  Purchase #3 $194.93   7.645%   $209.8324   $209.83   $209.85   $209.80  
  Purchase #4 $83.61   10.625%   $92.4936   $92.49   $92.50   $92.50  
  Purchase #5 $68.63   5.270%   $72.2468   $72.25   $72.25   $72.20  
  Purchase #6 $199.64   9.410%   $218.4261   $218.43   $218.45   $218.40  
  Purchase #7 $26.82   8.192%   $29.0171   $29.02   $29.00   $29.00  
  7 purchase totals = $747.93       $803.1300   $803.14   $803.15   $803.00