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 $31.74   3.855%   $32.9636   $32.96   $32.95   $33.00  
  Purchase #2 $54.85   13.572%   $62.2942   $62.29   $62.30   $62.30  
  Purchase #3 $208.61   6.531%   $222.2343   $222.23   $222.25   $222.20  
  Purchase #4 $225.82   4.440%   $235.8464   $235.85   $235.85   $235.80  
  Purchase #5 $198.68   3.483%   $205.6   $205.60   $205.60   $205.60  
  Purchase #6 $151.35   3.391%   $156.4823   $156.48   $156.50   $156.50  
  Purchase #7 $250.46   3.791%   $259.9549   $259.95   $259.95   $260.00  
  7 purchase totals = $1,121.51       $1,175.3757   $1,175.36   $1,175.40   $1,175.40