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 $214.36   4.642%   $224.3106   $224.31   $224.30   $224.30  
  Purchase #2 $111.56   12.647%   $125.669   $125.67   $125.65   $125.70  
  Purchase #3 $162.33   9.245%   $177.3374   $177.34   $177.35   $177.30  
  Purchase #4 $135.26   12.130%   $151.667   $151.67   $151.65   $151.70  
  Purchase #5 $190.92   7.198%   $204.6624   $204.66   $204.65   $204.70  
  Purchase #6 $237.68   11.431%   $264.8492   $264.85   $264.85   $264.80  
  Purchase #7 $70.66   7.458%   $75.9298   $75.93   $75.95   $75.90  
  7 purchase totals = $1,122.77       $1,224.4254   $1,224.43   $1,224.40   $1,224.40