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 $28.87   12.709%   $32.5391   $32.54   $32.55   $32.50  
  Purchase #2 $59.80   10.833%   $66.2781   $66.28   $66.30   $66.30  
  Purchase #3 $115.89   5.538%   $122.308   $122.31   $122.30   $122.30  
  Purchase #4 $195.43   3.733%   $202.7254   $202.73   $202.75   $202.70  
  Purchase #5 $242.52   4.770%   $254.0882   $254.09   $254.10   $254.10  
  Purchase #6 $197.32   5.247%   $207.6734   $207.67   $207.65   $207.70  
  Purchase #7 $157.94   5.735%   $166.9979   $167.00   $167.00   $167.00  
  7 purchase totals = $997.77       $1,052.6101   $1,052.62   $1,052.65   $1,052.60