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 $142.45   3.243%   $147.0697   $147.07   $147.05   $147.10  
  Purchase #2 $14.58   8.482%   $15.8167   $15.82   $15.80   $15.80  
  Purchase #3 $202.81   3.686%   $210.2856   $210.29   $210.30   $210.30  
  Purchase #4 $187.68   11.592%   $209.4359   $209.44   $209.45   $209.40  
  Purchase #5 $203.26   11.147%   $225.9174   $225.92   $225.90   $225.90  
  Purchase #6 $218.73   10.181%   $240.9989   $241.00   $241.00   $241.00  
  Purchase #7 $206.52   10.141%   $227.4632   $227.46   $227.45   $227.50  
  7 purchase totals = $1,176.03       $1,276.9874   $1,277.00   $1,276.95   $1,277.00