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 $59.68   13.483%   $67.7267   $67.73   $67.75   $67.70  
  Purchase #2 $53.69   11.183%   $59.6942   $59.69   $59.70   $59.70  
  Purchase #3 $188.34   9.382%   $206.0101   $206.01   $206.00   $206.00  
  Purchase #4 $229.64   6.139%   $243.7376   $243.74   $243.75   $243.70  
  Purchase #5 $199.55   10.458%   $220.4189   $220.42   $220.40   $220.40  
  Purchase #6 $23.80   4.122%   $24.781   $24.78   $24.80   $24.80  
  Purchase #7 $137.64   12.353%   $154.6427   $154.64   $154.65   $154.60  
  7 purchase totals = $892.34       $977.0112   $977.01   $977.05   $976.90