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 $226.62   11.354%   $252.3504   $252.35   $252.35   $252.40  
  Purchase #2 $151.25   10.308%   $166.8409   $166.84   $166.85   $166.80  
  Purchase #3 $115.91   13.282%   $131.3052   $131.31   $131.30   $131.30  
  Purchase #4 $40.83   9.563%   $44.7346   $44.73   $44.75   $44.70  
  Purchase #5 $88.67   9.197%   $96.825   $96.83   $96.85   $96.80  
  Purchase #6 $230.50   5.611%   $243.4334   $243.43   $243.45   $243.40  
  Purchase #7 $169.64   6.498%   $180.6632   $180.66   $180.65   $180.70  
  7 purchase totals = $1,023.42       $1,116.1527   $1,116.15   $1,116.20   $1,116.10