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 $56.72   6.574%   $60.4488   $60.45   $60.45   $60.40  
  Purchase #2 $192.26   9.348%   $210.2325   $210.23   $210.25   $210.20  
  Purchase #3 $246.51   12.424%   $277.1364   $277.14   $277.15   $277.10  
  Purchase #4 $101.83   5.742%   $107.6771   $107.68   $107.70   $107.70  
  Purchase #5 $106.75   11.873%   $119.4244   $119.42   $119.40   $119.40  
  Purchase #6 $184.59   4.459%   $192.8209   $192.82   $192.80   $192.80  
  Purchase #7 $185.57   13.593%   $210.7945   $210.79   $210.80   $210.80  
  7 purchase totals = $1,074.23       $1,178.5346   $1,178.53   $1,178.55   $1,178.40