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 $167.90   9.857%   $184.4499   $184.45   $184.45   $184.40  
  Purchase #2 $70.26   4.114%   $73.1505   $73.15   $73.15   $73.20  
  Purchase #3 $24.68   9.105%   $26.9271   $26.93   $26.95   $26.90  
  Purchase #4 $120.30   4.766%   $126.0335   $126.03   $126.05   $126.00  
  Purchase #5 $148.49   3.487%   $153.6678   $153.67   $153.65   $153.70  
  Purchase #6 $114.29   3.611%   $118.417   $118.42   $118.40   $118.40  
  Purchase #7 $235.78   12.262%   $264.6913   $264.69   $264.70   $264.70  
  7 purchase totals = $881.70       $947.3371   $947.34   $947.35   $947.30