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 $236.85   12.414%   $266.2526   $266.25   $266.25   $266.30  
  Purchase #2 $150.66   3.687%   $156.2148   $156.21   $156.20   $156.20  
  Purchase #3 $99.96   4.224%   $104.1823   $104.18   $104.20   $104.20  
  Purchase #4 $195.28   12.103%   $218.9147   $218.91   $218.90   $218.90  
  Purchase #5 $233.98   8.871%   $254.7364   $254.74   $254.75   $254.70  
  Purchase #6 $167.63   8.771%   $182.3328   $182.33   $182.35   $182.30  
  Purchase #7 $19.93   4.551%   $20.837   $20.84   $20.85   $20.80  
  7 purchase totals = $1,104.29       $1,203.4706   $1,203.46   $1,203.50   $1,203.40