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 $241.46   5.465%   $254.6558   $254.66   $254.65   $254.70  
  Purchase #2 $214.96   6.772%   $229.5171   $229.52   $229.50   $229.50  
  Purchase #3 $244.38   7.268%   $262.1415   $262.14   $262.15   $262.10  
  Purchase #4 $57.72   10.662%   $63.8741   $63.87   $63.85   $63.90  
  Purchase #5 $143.79   6.713%   $153.4426   $153.44   $153.45   $153.40  
  Purchase #6 $249.92   11.403%   $278.4184   $278.42   $278.40   $278.40  
  Purchase #7 $75.75   5.462%   $79.8875   $79.89   $79.90   $79.90  
  7 purchase totals = $1,227.98       $1,321.9370   $1,321.94   $1,321.90   $1,321.90