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 $243.89   10.612%   $269.7716   $269.77   $269.75   $269.80  
  Purchase #2 $138.49   4.426%   $144.6196   $144.62   $144.60   $144.60  
  Purchase #3 $210.88   4.486%   $220.3401   $220.34   $220.35   $220.30  
  Purchase #4 $21.67   11.451%   $24.1514   $24.15   $24.15   $24.20  
  Purchase #5 $52.78   5.426%   $55.6438   $55.64   $55.65   $55.60  
  Purchase #6 $206.88   3.279%   $213.6636   $213.66   $213.65   $213.70  
  Purchase #7 $114.65   9.191%   $125.1875   $125.19   $125.20   $125.20  
  7 purchase totals = $989.24       $1,053.3776   $1,053.37   $1,053.35   $1,053.40