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 $146.88   11.328%   $163.5186   $163.52   $163.50   $163.50  
  Purchase #2 $231.41   8.293%   $250.6008   $250.60   $250.60   $250.60  
  Purchase #3 $237.95   11.745%   $265.8972   $265.90   $265.90   $265.90  
  Purchase #4 $217.60   9.764%   $238.8465   $238.85   $238.85   $238.80  
  Purchase #5 $62.44   7.246%   $66.9644   $66.96   $66.95   $67.00  
  Purchase #6 $250.92   8.310%   $271.7715   $271.77   $271.75   $271.80  
  Purchase #7 $148.78   12.672%   $167.6334   $167.63   $167.65   $167.60  
  7 purchase totals = $1,295.98       $1,425.2324   $1,425.23   $1,425.20   $1,425.20