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 $239.70   13.460%   $271.9636   $271.96   $271.95   $272.00  
  Purchase #2 $64.80   10.544%   $71.6325   $71.63   $71.65   $71.60  
  Purchase #3 $200.66   9.845%   $220.415   $220.42   $220.40   $220.40  
  Purchase #4 $55.57   4.819%   $58.2479   $58.25   $58.25   $58.20  
  Purchase #5 $213.73   8.662%   $232.2433   $232.24   $232.25   $232.20  
  Purchase #6 $247.59   11.314%   $275.6023   $275.60   $275.60   $275.60  
  Purchase #7 $69.31   4.411%   $72.3673   $72.37   $72.35   $72.40  
  7 purchase totals = $1,091.36       $1,202.4719   $1,202.47   $1,202.45   $1,202.40