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 $246.72   8.863%   $268.5868   $268.59   $268.60   $268.60  
  Purchase #2 $186.48   5.227%   $196.2273   $196.23   $196.25   $196.20  
  Purchase #3 $80.91   9.309%   $88.4419   $88.44   $88.45   $88.40  
  Purchase #4 $194.71   8.257%   $210.7872   $210.79   $210.80   $210.80  
  Purchase #5 $116.93   7.401%   $125.584   $125.58   $125.60   $125.60  
  Purchase #6 $31.92   10.807%   $35.3696   $35.37   $35.35   $35.40  
  Purchase #7 $131.44   4.472%   $137.318   $137.32   $137.30   $137.30  
  7 purchase totals = $989.11       $1,062.3148   $1,062.32   $1,062.35   $1,062.30