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 $188.30   8.630%   $204.5503   $204.55   $204.55   $204.60  
  Purchase #2 $66.49   9.360%   $72.7135   $72.71   $72.70   $72.70  
  Purchase #3 $232.59   11.386%   $259.0727   $259.07   $259.05   $259.10  
  Purchase #4 $52.77   12.580%   $59.4085   $59.41   $59.40   $59.40  
  Purchase #5 $97.26   7.381%   $104.4388   $104.44   $104.45   $104.40  
  Purchase #6 $114.75   4.401%   $119.8001   $119.80   $119.80   $119.80  
  Purchase #7 $145.42   12.160%   $163.1031   $163.10   $163.10   $163.10  
  7 purchase totals = $897.58       $983.0870   $983.08   $983.05   $983.10