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 $214.97   8.169%   $232.5309   $232.53   $232.55   $232.50  
  Purchase #2 $67.53   10.277%   $74.4701   $74.47   $74.45   $74.50  
  Purchase #3 $216.96   11.127%   $241.1011   $241.10   $241.10   $241.10  
  Purchase #4 $112.93   13.479%   $128.1518   $128.15   $128.15   $128.20  
  Purchase #5 $19.69   6.568%   $20.9832   $20.98   $21.00   $21.00  
  Purchase #6 $61.33   4.129%   $63.8623   $63.86   $63.85   $63.90  
  Purchase #7 $60.42   7.390%   $64.885   $64.89   $64.90   $64.90  
  7 purchase totals = $753.83       $825.9844   $825.98   $826.00   $826.10