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 $86.76   3.384%   $89.696   $89.70   $89.70   $89.70  
  Purchase #2 $212.54   13.558%   $241.3562   $241.36   $241.35   $241.40  
  Purchase #3 $50.73   8.140%   $54.8594   $54.86   $54.85   $54.90  
  Purchase #4 $84.51   12.602%   $95.16   $95.16   $95.15   $95.20  
  Purchase #5 $175.70   4.351%   $183.3447   $183.34   $183.35   $183.30  
  Purchase #6 $181.97   13.513%   $206.5596   $206.56   $206.55   $206.60  
  Purchase #7 $231.98   9.172%   $253.2572   $253.26   $253.25   $253.30  
  7 purchase totals = $1,024.19       $1,124.2331   $1,124.24   $1,124.20   $1,124.40