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 $225.29   10.297%   $248.4881   $248.49   $248.50   $248.50  
  Purchase #2 $164.65   4.408%   $171.9078   $171.91   $171.90   $171.90  
  Purchase #3 $23.76   11.294%   $26.4435   $26.44   $26.45   $26.40  
  Purchase #4 $204.71   6.516%   $218.0489   $218.05   $218.05   $218.00  
  Purchase #5 $162.59   7.813%   $175.2932   $175.29   $175.30   $175.30  
  Purchase #6 $41.70   9.300%   $45.5781   $45.58   $45.60   $45.60  
  Purchase #7 $250.77   6.105%   $266.0795   $266.08   $266.10   $266.10  
  7 purchase totals = $1,073.47       $1,151.8391   $1,151.84   $1,151.90   $1,151.80