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 $62.76   9.476%   $68.7071   $68.71   $68.70   $68.70  
  Purchase #2 $57.33   11.315%   $63.8169   $63.82   $63.80   $63.80  
  Purchase #3 $127.77   7.746%   $137.6671   $137.67   $137.65   $137.70  
  Purchase #4 $171.91   7.683%   $185.1178   $185.12   $185.10   $185.10  
  Purchase #5 $230.72   9.520%   $252.6845   $252.68   $252.70   $252.70  
  Purchase #6 $193.60   5.180%   $203.6285   $203.63   $203.65   $203.60  
  Purchase #7 $141.31   9.546%   $154.7995   $154.80   $154.80   $154.80  
  7 purchase totals = $985.40       $1,066.4214   $1,066.43   $1,066.40   $1,066.40