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 $243.65   13.551%   $276.667   $276.67   $276.65   $276.70  
  Purchase #2 $221.59   3.747%   $229.893   $229.89   $229.90   $229.90  
  Purchase #3 $174.40   12.405%   $196.0343   $196.03   $196.05   $196.00  
  Purchase #4 $224.27   5.799%   $237.2754   $237.28   $237.30   $237.30  
  Purchase #5 $57.36   9.369%   $62.7341   $62.73   $62.75   $62.70  
  Purchase #6 $228.67   5.384%   $240.9816   $240.98   $241.00   $241.00  
  Purchase #7 $18.58   9.567%   $20.3575   $20.36   $20.35   $20.40  
  7 purchase totals = $1,168.52       $1,263.9429   $1,263.94   $1,264.00   $1,264.00