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 $65.58   4.202%   $68.3357   $68.34   $68.35   $68.30  
  Purchase #2 $219.47   6.349%   $233.4042   $233.40   $233.40   $233.40  
  Purchase #3 $202.33   12.416%   $227.4513   $227.45   $227.45   $227.50  
  Purchase #4 $238.27   3.292%   $246.1138   $246.11   $246.10   $246.10  
  Purchase #5 $33.47   5.151%   $35.194   $35.19   $35.20   $35.20  
  Purchase #6 $161.66   10.707%   $178.9689   $178.97   $178.95   $179.00  
  Purchase #7 $23.53   6.792%   $25.1282   $25.13   $25.15   $25.10  
  7 purchase totals = $944.31       $1,014.5961   $1,014.59   $1,014.60   $1,014.60