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 $167.77   9.404%   $183.5471   $183.55   $183.55   $183.50  
  Purchase #2 $59.27   6.472%   $63.106   $63.11   $63.10   $63.10  
  Purchase #3 $178.81   7.346%   $191.9454   $191.95   $191.95   $191.90  
  Purchase #4 $116.76   7.399%   $125.3991   $125.40   $125.40   $125.40  
  Purchase #5 $12.61   13.807%   $14.3511   $14.35   $14.35   $14.40  
  Purchase #6 $24.57   11.110%   $27.2997   $27.30   $27.30   $27.30  
  Purchase #7 $133.38   4.831%   $139.8236   $139.82   $139.80   $139.80  
  7 purchase totals = $693.17       $745.4720   $745.48   $745.45   $745.40