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 $133.72   13.701%   $152.041   $152.04   $152.05   $152.00  
  Purchase #2 $59.95   5.597%   $63.3054   $63.31   $63.30   $63.30  
  Purchase #3 $205.91   10.427%   $227.3802   $227.38   $227.40   $227.40  
  Purchase #4 $91.48   6.792%   $97.6933   $97.69   $97.70   $97.70  
  Purchase #5 $189.40   10.185%   $208.6904   $208.69   $208.70   $208.70  
  Purchase #6 $46.99   6.265%   $49.9339   $49.93   $49.95   $49.90  
  Purchase #7 $210.92   9.722%   $231.4256   $231.43   $231.45   $231.40  
  7 purchase totals = $938.37       $1,030.4698   $1,030.47   $1,030.55   $1,030.40