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 $204.65   13.204%   $231.672   $231.67   $231.65   $231.70  
  Purchase #2 $44.50   3.458%   $46.0388   $46.04   $46.05   $46.00  
  Purchase #3 $249.39   13.674%   $283.4916   $283.49   $283.50   $283.50  
  Purchase #4 $232.65   10.777%   $257.7227   $257.72   $257.70   $257.70  
  Purchase #5 $170.59   4.480%   $178.2324   $178.23   $178.25   $178.20  
  Purchase #6 $183.25   11.824%   $204.9175   $204.92   $204.90   $204.90  
  Purchase #7 $141.29   8.834%   $153.7716   $153.77   $153.75   $153.80  
  7 purchase totals = $1,226.32       $1,355.8466   $1,355.84   $1,355.80   $1,355.80