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 $70.78   6.766%   $75.569   $75.57   $75.55   $75.60  
  Purchase #2 $114.41   13.341%   $129.6734   $129.67   $129.65   $129.70  
  Purchase #3 $24.42   6.618%   $26.0361   $26.04   $26.05   $26.00  
  Purchase #4 $8.77   3.132%   $9.0447   $9.04   $9.05   $9.00  
  Purchase #5 $43.27   4.544%   $45.2362   $45.24   $45.25   $45.20  
  Purchase #6 $96.99   3.257%   $100.149   $100.15   $100.15   $100.10  
  Purchase #7 $245.59   12.423%   $276.0996   $276.10   $276.10   $276.10  
  7 purchase totals = $604.23       $661.8080   $661.81   $661.80   $661.70