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 $53.70   12.393%   $60.355   $60.36   $60.35   $60.40  
  Purchase #2 $153.97   13.221%   $174.3264   $174.33   $174.35   $174.30  
  Purchase #3 $146.79   9.228%   $160.3358   $160.34   $160.35   $160.30  
  Purchase #4 $238.25   12.242%   $267.4166   $267.42   $267.40   $267.40  
  Purchase #5 $185.93   8.602%   $201.9237   $201.92   $201.90   $201.90  
  Purchase #6 $232.72   9.342%   $254.4607   $254.46   $254.45   $254.50  
  Purchase #7 $229.65   7.466%   $246.7957   $246.80   $246.80   $246.80  
  7 purchase totals = $1,241.01       $1,365.6139   $1,365.63   $1,365.60   $1,365.60