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 $24.55   3.677%   $25.4527   $25.45   $25.45   $25.50  
  Purchase #2 $246.58   6.539%   $262.7039   $262.70   $262.70   $262.70  
  Purchase #3 $127.33   3.486%   $131.7687   $131.77   $131.75   $131.80  
  Purchase #4 $186.58   12.729%   $210.3298   $210.33   $210.35   $210.30  
  Purchase #5 $68.70   6.497%   $73.1634   $73.16   $73.15   $73.20  
  Purchase #6 $33.51   6.782%   $35.7826   $35.78   $35.80   $35.80  
  Purchase #7 $153.90   10.582%   $170.1857   $170.19   $170.20   $170.20  
  7 purchase totals = $841.15       $909.3868   $909.38   $909.40   $909.50