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 $128.84   8.553%   $139.8597   $139.86   $139.85   $139.90  
  Purchase #2 $85.75   13.585%   $97.3991   $97.40   $97.40   $97.40  
  Purchase #3 $20.51   13.598%   $23.2989   $23.30   $23.30   $23.30  
  Purchase #4 $244.97   11.467%   $273.0607   $273.06   $273.05   $273.10  
  Purchase #5 $58.84   8.155%   $63.6384   $63.64   $63.65   $63.60  
  Purchase #6 $207.73   5.834%   $219.849   $219.85   $219.85   $219.80  
  Purchase #7 $230.33   10.776%   $255.1504   $255.15   $255.15   $255.20  
  7 purchase totals = $976.97       $1,072.2562   $1,072.26   $1,072.25   $1,072.30