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 $241.99   13.757%   $275.2806   $275.28   $275.30   $275.30  
  Purchase #2 $31.49   6.107%   $33.4131   $33.41   $33.40   $33.40  
  Purchase #3 $37.68   9.306%   $41.1865   $41.19   $41.20   $41.20  
  Purchase #4 $98.85   3.587%   $102.3957   $102.40   $102.40   $102.40  
  Purchase #5 $42.41   10.584%   $46.8987   $46.90   $46.90   $46.90  
  Purchase #6 $152.53   4.180%   $158.9058   $158.91   $158.90   $158.90  
  Purchase #7 $206.41   8.273%   $223.4863   $223.49   $223.50   $223.50  
  7 purchase totals = $811.36       $881.5667   $881.58   $881.60   $881.60