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 $110.98   7.201%   $118.9717   $118.97   $118.95   $119.00  
  Purchase #2 $85.27   11.185%   $94.8074   $94.81   $94.80   $94.80  
  Purchase #3 $26.65   13.646%   $30.2867   $30.29   $30.30   $30.30  
  Purchase #4 $77.95   3.739%   $80.8646   $80.86   $80.85   $80.90  
  Purchase #5 $196.77   9.155%   $214.7843   $214.78   $214.80   $214.80  
  Purchase #6 $86.77   6.497%   $92.4074   $92.41   $92.40   $92.40  
  Purchase #7 $250.86   9.230%   $274.0144   $274.01   $274.00   $274.00  
  7 purchase totals = $835.25       $906.1365   $906.13   $906.10   $906.20