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 $132.76   12.698%   $149.6179   $149.62   $149.60   $149.60  
  Purchase #2 $203.28   10.555%   $224.7362   $224.74   $224.75   $224.70  
  Purchase #3 $147.93   13.129%   $167.3517   $167.35   $167.35   $167.40  
  Purchase #4 $196.86   4.768%   $206.2463   $206.25   $206.25   $206.20  
  Purchase #5 $199.93   4.299%   $208.525   $208.53   $208.55   $208.50  
  Purchase #6 $26.54   9.765%   $29.1316   $29.13   $29.15   $29.10  
  Purchase #7 $206.58   5.707%   $218.3695   $218.37   $218.35   $218.40  
  7 purchase totals = $1,113.88       $1,203.9782   $1,203.99   $1,204.00   $1,203.90