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 $66.53   4.586%   $69.5811   $69.58   $69.60   $69.60  
  Purchase #2 $158.50   12.367%   $178.1017   $178.10   $178.10   $178.10  
  Purchase #3 $112.60   9.298%   $123.0695   $123.07   $123.05   $123.10  
  Purchase #4 $31.78   10.198%   $35.0209   $35.02   $35.00   $35.00  
  Purchase #5 $236.75   6.453%   $252.0275   $252.03   $252.05   $252.00  
  Purchase #6 $189.57   12.692%   $213.6302   $213.63   $213.65   $213.60  
  Purchase #7 $110.53   11.301%   $123.021   $123.02   $123.00   $123.00  
  7 purchase totals = $906.26       $994.4519   $994.45   $994.45   $994.40