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 $87.44   12.180%   $98.0902   $98.09   $98.10   $98.10  
  Purchase #2 $33.70   7.718%   $36.301   $36.30   $36.30   $36.30  
  Purchase #3 $41.42   11.107%   $46.0205   $46.02   $46.00   $46.00  
  Purchase #4 $249.64   7.278%   $267.8088   $267.81   $267.80   $267.80  
  Purchase #5 $45.57   10.257%   $50.2441   $50.24   $50.25   $50.20  
  Purchase #6 $56.50   4.792%   $59.2075   $59.21   $59.20   $59.20  
  Purchase #7 $164.57   8.225%   $178.1059   $178.11   $178.10   $178.10  
  7 purchase totals = $678.84       $735.7780   $735.78   $735.75   $735.70