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 $145.79   10.761%   $161.4785   $161.48   $161.50   $161.50  
  Purchase #2 $244.39   9.199%   $266.8714   $266.87   $266.85   $266.90  
  Purchase #3 $156.39   6.142%   $165.9955   $166.00   $166.00   $166.00  
  Purchase #4 $246.39   3.628%   $255.329   $255.33   $255.35   $255.30  
  Purchase #5 $101.80   12.775%   $114.805   $114.81   $114.80   $114.80  
  Purchase #6 $177.46   4.138%   $184.8033   $184.80   $184.80   $184.80  
  Purchase #7 $137.90   13.387%   $156.3607   $156.36   $156.35   $156.40  
  7 purchase totals = $1,210.12       $1,305.6434   $1,305.65   $1,305.65   $1,305.70