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 $163.33   13.662%   $185.6441   $185.64   $185.65   $185.60  
  Purchase #2 $99.68   8.140%   $107.794   $107.79   $107.80   $107.80  
  Purchase #3 $148.35   8.170%   $160.4702   $160.47   $160.45   $160.50  
  Purchase #4 $121.76   10.455%   $134.49   $134.49   $134.50   $134.50  
  Purchase #5 $115.46   9.565%   $126.5037   $126.50   $126.50   $126.50  
  Purchase #6 $218.44   9.376%   $238.9209   $238.92   $238.90   $238.90  
  Purchase #7 $102.48   12.591%   $115.3833   $115.38   $115.40   $115.40  
  7 purchase totals = $969.50       $1,069.2062   $1,069.19   $1,069.20   $1,069.20