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 $214.49   9.828%   $235.5701   $235.57   $235.55   $235.60  
  Purchase #2 $140.33   13.466%   $159.2268   $159.23   $159.25   $159.20  
  Purchase #3 $110.86   7.543%   $119.2222   $119.22   $119.20   $119.20  
  Purchase #4 $128.76   3.535%   $133.3117   $133.31   $133.30   $133.30  
  Purchase #5 $33.85   10.184%   $37.2973   $37.30   $37.30   $37.30  
  Purchase #6 $192.91   8.445%   $209.2012   $209.20   $209.20   $209.20  
  Purchase #7 $56.25   4.821%   $58.9618   $58.96   $58.95   $59.00  
  7 purchase totals = $877.45       $952.7911   $952.79   $952.75   $952.80