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 $72.48   13.858%   $82.5243   $82.52   $82.50   $82.50  
  Purchase #2 $159.85   6.322%   $169.9557   $169.96   $169.95   $170.00  
  Purchase #3 $182.44   10.429%   $201.4667   $201.47   $201.45   $201.50  
  Purchase #4 $217.97   6.416%   $231.955   $231.96   $231.95   $232.00  
  Purchase #5 $206.37   12.832%   $232.8514   $232.85   $232.85   $232.90  
  Purchase #6 $132.66   5.139%   $139.4774   $139.48   $139.50   $139.50  
  Purchase #7 $15.58   3.544%   $16.1322   $16.13   $16.15   $16.10  
  7 purchase totals = $987.35       $1,074.3627   $1,074.37   $1,074.35   $1,074.50