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 $81.46   4.661%   $85.2569   $85.26   $85.25   $85.30  
  Purchase #2 $60.49   9.656%   $66.3309   $66.33   $66.35   $66.30  
  Purchase #3 $96.96   6.540%   $103.3012   $103.30   $103.30   $103.30  
  Purchase #4 $15.55   13.304%   $17.6188   $17.62   $17.60   $17.60  
  Purchase #5 $205.54   4.431%   $214.6475   $214.65   $214.65   $214.60  
  Purchase #6 $93.56   8.478%   $101.492   $101.49   $101.50   $101.50  
  Purchase #7 $6.46   5.505%   $6.8156   $6.82   $6.80   $6.80  
  7 purchase totals = $560.02       $595.4629   $595.47   $595.45   $595.40