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 $88.96   5.262%   $93.6411   $93.64   $93.65   $93.60  
  Purchase #2 $228.41   13.676%   $259.6474   $259.65   $259.65   $259.60  
  Purchase #3 $210.87   4.257%   $219.8467   $219.85   $219.85   $219.80  
  Purchase #4 $19.88   6.227%   $21.1179   $21.12   $21.10   $21.10  
  Purchase #5 $146.97   3.255%   $151.7539   $151.75   $151.75   $151.80  
  Purchase #6 $231.96   8.760%   $252.2797   $252.28   $252.30   $252.30  
  Purchase #7 $156.69   4.278%   $163.3932   $163.39   $163.40   $163.40  
  7 purchase totals = $1,083.74       $1,161.6799   $1,161.68   $1,161.70   $1,161.60