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 $135.50   9.281%   $148.0758   $148.08   $148.10   $148.10  
  Purchase #2 $109.40   4.262%   $114.0626   $114.06   $114.05   $114.10  
  Purchase #3 $236.99   10.184%   $261.1251   $261.13   $261.15   $261.10  
  Purchase #4 $72.52   10.457%   $80.1034   $80.10   $80.10   $80.10  
  Purchase #5 $18.46   9.627%   $20.2371   $20.24   $20.25   $20.20  
  Purchase #6 $63.76   7.665%   $68.6472   $68.65   $68.65   $68.60  
  Purchase #7 $133.64   8.775%   $145.3669   $145.37   $145.35   $145.40  
  7 purchase totals = $770.27       $837.6181   $837.63   $837.65   $837.60