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 $206.59   13.808%   $235.1159   $235.12   $235.10   $235.10  
  Purchase #2 $219.31   13.750%   $249.4651   $249.47   $249.45   $249.50  
  Purchase #3 $226.29   13.130%   $256.0019   $256.00   $256.00   $256.00  
  Purchase #4 $8.53   11.862%   $9.5418   $9.54   $9.55   $9.50  
  Purchase #5 $119.65   5.275%   $125.9615   $125.96   $125.95   $126.00  
  Purchase #6 $35.59   12.677%   $40.1017   $40.10   $40.10   $40.10  
  Purchase #7 $88.82   6.603%   $94.6848   $94.68   $94.70   $94.70  
  7 purchase totals = $904.78       $1,010.8727   $1,010.87   $1,010.85   $1,010.90