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 $148.51   6.140%   $157.6285   $157.63   $157.65   $157.60  
  Purchase #2 $117.84   8.420%   $127.7621   $127.76   $127.75   $127.80  
  Purchase #3 $218.70   9.138%   $238.6848   $238.68   $238.70   $238.70  
  Purchase #4 $220.92   6.675%   $235.6664   $235.67   $235.65   $235.70  
  Purchase #5 $95.87   8.820%   $104.3257   $104.33   $104.35   $104.30  
  Purchase #6 $201.55   11.698%   $225.1273   $225.13   $225.15   $225.10  
  Purchase #7 $244.33   6.190%   $259.454   $259.45   $259.45   $259.50  
  7 purchase totals = $1,247.72       $1,348.6488   $1,348.65   $1,348.70   $1,348.70