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 $95.44   3.128%   $98.4254   $98.43   $98.45   $98.40  
  Purchase #2 $207.97   10.618%   $230.0523   $230.05   $230.05   $230.10  
  Purchase #3 $160.45   7.487%   $172.4629   $172.46   $172.45   $172.50  
  Purchase #4 $219.51   6.250%   $233.2294   $233.23   $233.25   $233.20  
  Purchase #5 $51.58   10.182%   $56.8319   $56.83   $56.85   $56.80  
  Purchase #6 $91.94   5.502%   $96.9985   $97.00   $97.00   $97.00  
  Purchase #7 $12.46   9.812%   $13.6826   $13.68   $13.70   $13.70  
  7 purchase totals = $839.35       $901.6830   $901.68   $901.75   $901.70