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 $107.41   6.384%   $114.2671   $114.27   $114.25   $114.30  
  Purchase #2 $194.51   10.687%   $215.2973   $215.30   $215.30   $215.30  
  Purchase #3 $138.84   10.735%   $153.7445   $153.74   $153.75   $153.70  
  Purchase #4 $195.63   8.481%   $212.2214   $212.22   $212.20   $212.20  
  Purchase #5 $94.32   12.448%   $106.061   $106.06   $106.05   $106.10  
  Purchase #6 $89.31   4.623%   $93.4388   $93.44   $93.45   $93.40  
  Purchase #7 $117.58   3.526%   $121.7259   $121.73   $121.75   $121.70  
  7 purchase totals = $937.60       $1,016.7560   $1,016.76   $1,016.75   $1,016.70