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 $84.90   9.635%   $93.0801   $93.08   $93.10   $93.10  
  Purchase #2 $199.81   13.276%   $226.3368   $226.34   $226.35   $226.30  
  Purchase #3 $119.93   9.521%   $131.3485   $131.35   $131.35   $131.30  
  Purchase #4 $204.79   4.385%   $213.77   $213.77   $213.75   $213.80  
  Purchase #5 $174.27   6.235%   $185.1357   $185.14   $185.15   $185.10  
  Purchase #6 $26.67   8.377%   $28.9041   $28.90   $28.90   $28.90  
  Purchase #7 $122.95   8.653%   $133.5889   $133.59   $133.60   $133.60  
  7 purchase totals = $933.32       $1,012.1641   $1,012.17   $1,012.20   $1,012.10