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 $211.93   9.788%   $232.6737   $232.67   $232.65   $232.70  
  Purchase #2 $150.97   11.662%   $168.5761   $168.58   $168.60   $168.60  
  Purchase #3 $246.36   3.825%   $255.7833   $255.78   $255.80   $255.80  
  Purchase #4 $73.97   5.122%   $77.7587   $77.76   $77.75   $77.80  
  Purchase #5 $134.80   13.634%   $153.1786   $153.18   $153.20   $153.20  
  Purchase #6 $100.41   8.501%   $108.9459   $108.95   $108.95   $108.90  
  Purchase #7 $25.77   9.848%   $28.3078   $28.31   $28.30   $28.30  
  7 purchase totals = $944.21       $1,025.2241   $1,025.23   $1,025.25   $1,025.30