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 $206.68   13.614%   $234.8174   $234.82   $234.80   $234.80  
  Purchase #2 $201.62   5.410%   $212.5276   $212.53   $212.55   $212.50  
  Purchase #3 $23.54   4.516%   $24.6031   $24.60   $24.60   $24.60  
  Purchase #4 $249.64   9.541%   $273.4582   $273.46   $273.45   $273.50  
  Purchase #5 $146.80   12.827%   $165.63   $165.63   $165.65   $165.60  
  Purchase #6 $98.39   7.581%   $105.8489   $105.85   $105.85   $105.80  
  Purchase #7 $169.88   8.453%   $184.24   $184.24   $184.25   $184.20  
  7 purchase totals = $1,096.55       $1,201.1252   $1,201.13   $1,201.15   $1,201.00