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 $66.67   4.635%   $69.7602   $69.76   $69.75   $69.80  
  Purchase #2 $238.33   11.619%   $266.0216   $266.02   $266.00   $266.00  
  Purchase #3 $56.30   9.592%   $61.7003   $61.70   $61.70   $61.70  
  Purchase #4 $155.48   13.814%   $176.958   $176.96   $176.95   $177.00  
  Purchase #5 $141.81   4.462%   $148.1376   $148.14   $148.15   $148.10  
  Purchase #6 $83.85   12.105%   $94   $94.00   $94.00   $94.00  
  Purchase #7 $226.34   12.172%   $253.8901   $253.89   $253.90   $253.90  
  7 purchase totals = $968.78       $1,070.4678   $1,070.47   $1,070.45   $1,070.50