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 $67.59   13.554%   $76.7511   $76.75   $76.75   $76.80  
  Purchase #2 $62.84   10.106%   $69.1906   $69.19   $69.20   $69.20  
  Purchase #3 $243.94   7.657%   $262.6185   $262.62   $262.60   $262.60  
  Purchase #4 $168.31   13.170%   $190.4764   $190.48   $190.50   $190.50  
  Purchase #5 $155.75   10.674%   $172.3748   $172.37   $172.35   $172.40  
  Purchase #6 $210.64   9.188%   $229.9936   $229.99   $230.00   $230.00  
  Purchase #7 $225.93   4.231%   $235.4891   $235.49   $235.50   $235.50  
  7 purchase totals = $1,135.00       $1,236.8941   $1,236.89   $1,236.90   $1,237.00