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 $18.33   13.780%   $20.8559   $20.86   $20.85   $20.90  
  Purchase #2 $195.89   12.826%   $221.0149   $221.01   $221.00   $221.00  
  Purchase #3 $187.97   11.410%   $209.4174   $209.42   $209.40   $209.40  
  Purchase #4 $216.59   9.746%   $237.6989   $237.70   $237.70   $237.70  
  Purchase #5 $149.56   9.160%   $163.2597   $163.26   $163.25   $163.30  
  Purchase #6 $192.36   11.184%   $213.8735   $213.87   $213.85   $213.90  
  Purchase #7 $174.33   3.218%   $179.9399   $179.94   $179.95   $179.90  
  7 purchase totals = $1,135.03       $1,246.0602   $1,246.06   $1,246.00   $1,246.10