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 $55.37   13.537%   $62.8654   $62.87   $62.85   $62.90  
  Purchase #2 $213.28   6.308%   $226.7337   $226.73   $226.75   $226.70  
  Purchase #3 $201.44   7.765%   $217.0818   $217.08   $217.10   $217.10  
  Purchase #4 $104.71   7.148%   $112.1947   $112.19   $112.20   $112.20  
  Purchase #5 $87.31   6.811%   $93.2567   $93.26   $93.25   $93.30  
  Purchase #6 $222.83   7.623%   $239.8163   $239.82   $239.80   $239.80  
  Purchase #7 $95.52   5.679%   $100.9446   $100.94   $100.95   $100.90  
  7 purchase totals = $980.46       $1,052.8932   $1,052.89   $1,052.90   $1,052.90