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 $227.91   8.342%   $246.9223   $246.92   $246.90   $246.90  
  Purchase #2 $206.90   11.144%   $229.9569   $229.96   $229.95   $230.00  
  Purchase #3 $194.56   11.827%   $217.5706   $217.57   $217.55   $217.60  
  Purchase #4 $206.34   9.417%   $225.771   $225.77   $225.75   $225.80  
  Purchase #5 $211.95   9.392%   $231.8563   $231.86   $231.85   $231.90  
  Purchase #6 $9.54   8.763%   $10.376   $10.38   $10.40   $10.40  
  Purchase #7 $90.72   8.511%   $98.4412   $98.44   $98.45   $98.40  
  7 purchase totals = $1,147.92       $1,260.8943   $1,260.90   $1,260.85   $1,261.00