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 $224.73   9.582%   $246.2636   $246.26   $246.25   $246.30  
  Purchase #2 $240.26   3.113%   $247.7393   $247.74   $247.75   $247.70  
  Purchase #3 $93.77   12.365%   $105.3647   $105.36   $105.35   $105.40  
  Purchase #4 $12.84   8.413%   $13.9202   $13.92   $13.90   $13.90  
  Purchase #5 $175.39   11.651%   $195.8247   $195.82   $195.80   $195.80  
  Purchase #6 $135.37   7.387%   $145.3698   $145.37   $145.35   $145.40  
  Purchase #7 $13.60   9.400%   $14.8784   $14.88   $14.90   $14.90  
  7 purchase totals = $895.96       $969.3607   $969.35   $969.30   $969.40