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 $218.69   8.287%   $236.8128   $236.81   $236.80   $236.80  
  Purchase #2 $118.89   7.327%   $127.6011   $127.60   $127.60   $127.60  
  Purchase #3 $41.45   7.765%   $44.6686   $44.67   $44.65   $44.70  
  Purchase #4 $133.96   11.733%   $149.6775   $149.68   $149.70   $149.70  
  Purchase #5 $169.50   6.604%   $180.6938   $180.69   $180.70   $180.70  
  Purchase #6 $109.83   4.846%   $115.1524   $115.15   $115.15   $115.20  
  Purchase #7 $103.93   12.187%   $116.5959   $116.60   $116.60   $116.60  
  7 purchase totals = $896.25       $971.2021   $971.20   $971.20   $971.30