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 $217.81   8.463%   $236.2433   $236.24   $236.25   $236.20  
  Purchase #2 $131.46   13.840%   $149.6541   $149.65   $149.65   $149.70  
  Purchase #3 $116.48   9.194%   $127.1892   $127.19   $127.20   $127.20  
  Purchase #4 $30.31   11.730%   $33.8654   $33.87   $33.85   $33.90  
  Purchase #5 $149.93   12.576%   $168.7852   $168.79   $168.80   $168.80  
  Purchase #6 $107.31   10.760%   $118.8566   $118.86   $118.85   $118.90  
  Purchase #7 $180.35   8.240%   $195.2108   $195.21   $195.20   $195.20  
  7 purchase totals = $933.65       $1,029.8046   $1,029.81   $1,029.80   $1,029.90