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 $200.36   11.317%   $223.0347   $223.03   $223.05   $223.00  
  Purchase #2 $131.88   10.841%   $146.1771   $146.18   $146.20   $146.20  
  Purchase #3 $231.91   9.255%   $253.3733   $253.37   $253.35   $253.40  
  Purchase #4 $182.32   8.232%   $197.3286   $197.33   $197.35   $197.30  
  Purchase #5 $240.88   10.121%   $265.2595   $265.26   $265.25   $265.30  
  Purchase #6 $111.32   7.194%   $119.3284   $119.33   $119.35   $119.30  
  Purchase #7 $201.64   4.203%   $210.1149   $210.11   $210.10   $210.10  
  7 purchase totals = $1,300.31       $1,414.6165   $1,414.61   $1,414.65   $1,414.60