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 $209.72   7.695%   $225.858   $225.86   $225.85   $225.90  
  Purchase #2 $101.26   12.109%   $113.5216   $113.52   $113.50   $113.50  
  Purchase #3 $25.58   10.659%   $28.3066   $28.31   $28.30   $28.30  
  Purchase #4 $100.45   8.569%   $109.0576   $109.06   $109.05   $109.10  
  Purchase #5 $161.70   13.436%   $183.426   $183.43   $183.45   $183.40  
  Purchase #6 $54.97   9.151%   $60.0003   $60.00   $60.00   $60.00  
  Purchase #7 $126.77   5.664%   $133.9503   $133.95   $133.95   $134.00  
  7 purchase totals = $780.45       $854.1204   $854.13   $854.10   $854.20