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 $233.60   13.247%   $264.545   $264.55   $264.55   $264.50  
  Purchase #2 $73.73   13.652%   $83.7956   $83.80   $83.80   $83.80  
  Purchase #3 $17.75   12.833%   $20.0279   $20.03   $20.05   $20.00  
  Purchase #4 $228.40   11.521%   $254.714   $254.71   $254.70   $254.70  
  Purchase #5 $111.92   7.176%   $119.9514   $119.95   $119.95   $120.00  
  Purchase #6 $215.90   9.279%   $235.9334   $235.93   $235.95   $235.90  
  Purchase #7 $50.92   6.785%   $54.3749   $54.37   $54.35   $54.40  
  7 purchase totals = $932.22       $1,033.3422   $1,033.34   $1,033.35   $1,033.30