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 $68.28   10.636%   $75.5423   $75.54   $75.55   $75.50  
  Purchase #2 $198.92   13.729%   $226.2297   $226.23   $226.25   $226.20  
  Purchase #3 $13.47   9.213%   $14.711   $14.71   $14.70   $14.70  
  Purchase #4 $96.85   9.297%   $105.8541   $105.85   $105.85   $105.90  
  Purchase #5 $117.80   10.653%   $130.3492   $130.35   $130.35   $130.30  
  Purchase #6 $206.48   10.420%   $227.9952   $228.00   $228.00   $228.00  
  Purchase #7 $5.32   4.479%   $5.5583   $5.56   $5.55   $5.60  
  7 purchase totals = $707.12       $786.2398   $786.24   $786.25   $786.20