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 $125.65   6.652%   $134.0082   $134.01   $134.00   $134.00  
  Purchase #2 $108.94   8.626%   $118.3372   $118.34   $118.35   $118.30  
  Purchase #3 $61.33   9.453%   $67.1275   $67.13   $67.15   $67.10  
  Purchase #4 $35.51   10.243%   $39.1473   $39.15   $39.15   $39.10  
  Purchase #5 $112.86   11.453%   $125.7859   $125.79   $125.80   $125.80  
  Purchase #6 $163.85   11.367%   $182.4748   $182.47   $182.45   $182.50  
  Purchase #7 $168.83   10.821%   $187.0991   $187.10   $187.10   $187.10  
  7 purchase totals = $776.97       $853.9800   $853.99   $854.00   $853.90