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 $55.62   8.735%   $60.4784   $60.48   $60.50   $60.50  
  Purchase #2 $140.85   13.495%   $159.8577   $159.86   $159.85   $159.90  
  Purchase #3 $181.72   11.526%   $202.665   $202.67   $202.65   $202.70  
  Purchase #4 $174.74   13.570%   $198.4522   $198.45   $198.45   $198.50  
  Purchase #5 $195.74   5.608%   $206.7171   $206.72   $206.70   $206.70  
  Purchase #6 $195.33   4.819%   $204.743   $204.74   $204.75   $204.70  
  Purchase #7 $38.47   11.162%   $42.764   $42.76   $42.75   $42.80  
  7 purchase totals = $982.47       $1,075.6774   $1,075.68   $1,075.65   $1,075.80