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 $248.51   10.110%   $273.6344   $273.63   $273.65   $273.60  
  Purchase #2 $150.31   7.495%   $161.5757   $161.58   $161.60   $161.60  
  Purchase #3 $187.43   11.552%   $209.0819   $209.08   $209.10   $209.10  
  Purchase #4 $90.82   5.609%   $95.9141   $95.91   $95.90   $95.90  
  Purchase #5 $33.96   7.135%   $36.383   $36.38   $36.40   $36.40  
  Purchase #6 $18.50   11.761%   $20.6758   $20.68   $20.70   $20.70  
  Purchase #7 $204.36   5.173%   $214.9315   $214.93   $214.95   $214.90  
  7 purchase totals = $933.89       $1,012.1964   $1,012.19   $1,012.30   $1,012.20