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 $122.35   6.542%   $130.3541   $130.35   $130.35   $130.40  
  Purchase #2 $118.59   6.665%   $126.494   $126.49   $126.50   $126.50  
  Purchase #3 $241.26   8.728%   $262.3172   $262.32   $262.30   $262.30  
  Purchase #4 $210.44   6.164%   $223.4115   $223.41   $223.40   $223.40  
  Purchase #5 $112.54   3.818%   $116.8368   $116.84   $116.85   $116.80  
  Purchase #6 $37.40   11.344%   $41.6427   $41.64   $41.65   $41.60  
  Purchase #7 $17.88   7.491%   $19.2194   $19.22   $19.20   $19.20  
  7 purchase totals = $860.46       $920.2757   $920.27   $920.25   $920.20