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 $64.27   5.854%   $68.0324   $68.03   $68.05   $68.00  
  Purchase #2 $34.54   3.708%   $35.8207   $35.82   $35.80   $35.80  
  Purchase #3 $16.45   10.472%   $18.1726   $18.17   $18.15   $18.20  
  Purchase #4 $26.45   11.125%   $29.3926   $29.39   $29.40   $29.40  
  Purchase #5 $66.42   13.209%   $75.1934   $75.19   $75.20   $75.20  
  Purchase #6 $226.75   6.252%   $240.9264   $240.93   $240.95   $240.90  
  Purchase #7 $10.31   5.191%   $10.8452   $10.85   $10.85   $10.80  
  7 purchase totals = $445.19       $478.3833   $478.38   $478.40   $478.30