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 $47.37   10.156%   $52.1809   $52.18   $52.20   $52.20  
  Purchase #2 $150.82   7.417%   $162.0063   $162.01   $162.00   $162.00  
  Purchase #3 $182.37   8.356%   $197.6088   $197.61   $197.60   $197.60  
  Purchase #4 $82.73   5.410%   $87.2057   $87.21   $87.20   $87.20  
  Purchase #5 $55.75   5.139%   $58.615   $58.62   $58.60   $58.60  
  Purchase #6 $182.50   7.488%   $196.1656   $196.17   $196.15   $196.20  
  Purchase #7 $201.41   11.831%   $225.2388   $225.24   $225.25   $225.20  
  7 purchase totals = $902.95       $979.0211   $979.04   $979.00   $979.00