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 $159.69   10.782%   $176.9078   $176.91   $176.90   $176.90  
  Purchase #2 $166.51   6.321%   $177.0351   $177.04   $177.05   $177.00  
  Purchase #3 $213.88   4.219%   $222.9036   $222.90   $222.90   $222.90  
  Purchase #4 $66.65   7.106%   $71.3861   $71.39   $71.40   $71.40  
  Purchase #5 $210.69   11.653%   $235.2417   $235.24   $235.25   $235.20  
  Purchase #6 $66.73   10.380%   $73.6566   $73.66   $73.65   $73.70  
  Purchase #7 $64.62   4.607%   $67.597   $67.60   $67.60   $67.60  
  7 purchase totals = $948.77       $1,024.7279   $1,024.74   $1,024.75   $1,024.70