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 $229.53   8.182%   $248.3101   $248.31   $248.30   $248.30  
  Purchase #2 $218.31   11.141%   $242.6319   $242.63   $242.65   $242.60  
  Purchase #3 $121.52   6.214%   $129.0713   $129.07   $129.05   $129.10  
  Purchase #4 $138.88   10.237%   $153.0971   $153.10   $153.10   $153.10  
  Purchase #5 $228.37   11.566%   $254.7833   $254.78   $254.80   $254.80  
  Purchase #6 $47.83   12.580%   $53.847   $53.85   $53.85   $53.80  
  Purchase #7 $150.76   10.232%   $166.1858   $166.19   $166.20   $166.20  
  7 purchase totals = $1,135.20       $1,247.9265   $1,247.93   $1,247.95   $1,247.90