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 $139.55   8.249%   $151.0615   $151.06   $151.05   $151.10  
  Purchase #2 $184.47   5.554%   $194.7155   $194.72   $194.70   $194.70  
  Purchase #3 $197.82   4.630%   $206.9791   $206.98   $207.00   $207.00  
  Purchase #4 $222.30   6.804%   $237.4253   $237.43   $237.45   $237.40  
  Purchase #5 $59.27   4.636%   $62.0178   $62.02   $62.00   $62.00  
  Purchase #6 $34.86   11.104%   $38.7309   $38.73   $38.75   $38.70  
  Purchase #7 $201.75   11.863%   $225.6836   $225.68   $225.70   $225.70  
  7 purchase totals = $1,040.02       $1,116.6137   $1,116.62   $1,116.65   $1,116.60