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 $242.67   11.180%   $269.8005   $269.80   $269.80   $269.80  
  Purchase #2 $56.64   8.222%   $61.2969   $61.30   $61.30   $61.30  
  Purchase #3 $222.88   13.593%   $253.1761   $253.18   $253.20   $253.20  
  Purchase #4 $32.93   6.169%   $34.9615   $34.96   $34.95   $35.00  
  Purchase #5 $126.26   5.734%   $133.4997   $133.50   $133.50   $133.50  
  Purchase #6 $138.38   9.844%   $152.0021   $152.00   $152.00   $152.00  
  Purchase #7 $153.61   6.662%   $163.8435   $163.84   $163.85   $163.80  
  7 purchase totals = $973.37       $1,068.5803   $1,068.58   $1,068.60   $1,068.60