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 $216.55   10.257%   $238.7615   $238.76   $238.75   $238.80  
  Purchase #2 $179.53   12.602%   $202.1544   $202.15   $202.15   $202.20  
  Purchase #3 $51.26   8.455%   $55.594   $55.59   $55.60   $55.60  
  Purchase #4 $85.52   10.176%   $94.2225   $94.22   $94.20   $94.20  
  Purchase #5 $249.72   7.817%   $269.2406   $269.24   $269.25   $269.20  
  Purchase #6 $27.47   5.444%   $28.9655   $28.97   $28.95   $29.00  
  Purchase #7 $58.88   3.770%   $61.0998   $61.10   $61.10   $61.10  
  7 purchase totals = $868.93       $950.0383   $950.03   $950.00   $950.10