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 $54.34   6.366%   $57.7993   $57.80   $57.80   $57.80  
  Purchase #2 $183.54   5.610%   $193.8366   $193.84   $193.85   $193.80  
  Purchase #3 $62.90   5.291%   $66.228   $66.23   $66.25   $66.20  
  Purchase #4 $174.89   8.194%   $189.2205   $189.22   $189.20   $189.20  
  Purchase #5 $211.60   12.762%   $238.6044   $238.60   $238.60   $238.60  
  Purchase #6 $119.52   8.297%   $129.4366   $129.44   $129.45   $129.40  
  Purchase #7 $119.62   10.752%   $132.4815   $132.48   $132.50   $132.50  
  7 purchase totals = $926.41       $1,007.6069   $1,007.61   $1,007.65   $1,007.50