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 $230.83   12.601%   $259.9169   $259.92   $259.90   $259.90  
  Purchase #2 $170.98   7.824%   $184.3575   $184.36   $184.35   $184.40  
  Purchase #3 $185.28   4.433%   $193.4935   $193.49   $193.50   $193.50  
  Purchase #4 $56.34   7.581%   $60.6111   $60.61   $60.60   $60.60  
  Purchase #5 $225.74   11.308%   $251.2667   $251.27   $251.25   $251.30  
  Purchase #6 $126.98   11.460%   $141.5319   $141.53   $141.55   $141.50  
  Purchase #7 $55.25   11.787%   $61.7623   $61.76   $61.75   $61.80  
  7 purchase totals = $1,051.40       $1,152.9399   $1,152.94   $1,152.90   $1,153.00