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 $136.75   11.164%   $152.0168   $152.02   $152.00   $152.00  
  Purchase #2 $146.66   11.128%   $162.9803   $162.98   $163.00   $163.00  
  Purchase #3 $247.27   11.857%   $276.5888   $276.59   $276.60   $276.60  
  Purchase #4 $112.26   3.573%   $116.271   $116.27   $116.25   $116.30  
  Purchase #5 $225.58   9.716%   $247.4974   $247.50   $247.50   $247.50  
  Purchase #6 $191.26   6.522%   $203.734   $203.73   $203.75   $203.70  
  Purchase #7 $213.68   3.488%   $221.1332   $221.13   $221.15   $221.10  
  7 purchase totals = $1,273.46       $1,380.2215   $1,380.22   $1,380.25   $1,380.20