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 $247.59   11.151%   $275.1988   $275.20   $275.20   $275.20  
  Purchase #2 $64.46   9.542%   $70.6108   $70.61   $70.60   $70.60  
  Purchase #3 $211.94   13.694%   $240.9631   $240.96   $240.95   $241.00  
  Purchase #4 $59.37   6.345%   $63.137   $63.14   $63.15   $63.10  
  Purchase #5 $158.26   11.685%   $176.7527   $176.75   $176.75   $176.80  
  Purchase #6 $81.81   11.516%   $91.2312   $91.23   $91.25   $91.20  
  Purchase #7 $217.29   11.235%   $241.7025   $241.70   $241.70   $241.70  
  7 purchase totals = $1,040.72       $1,159.5961   $1,159.59   $1,159.60   $1,159.60