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 $59.45   8.831%   $64.7   $64.70   $64.70   $64.70  
  Purchase #2 $225.75   11.795%   $252.3772   $252.38   $252.40   $252.40  
  Purchase #3 $44.81   6.268%   $47.6187   $47.62   $47.60   $47.60  
  Purchase #4 $206.94   11.356%   $230.4401   $230.44   $230.45   $230.40  
  Purchase #5 $96.57   4.427%   $100.8452   $100.85   $100.85   $100.80  
  Purchase #6 $49.94   9.558%   $54.7133   $54.71   $54.70   $54.70  
  Purchase #7 $227.99   3.793%   $236.6377   $236.64   $236.65   $236.60  
  7 purchase totals = $911.45       $987.3322   $987.34   $987.35   $987.20