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 $94.34   9.843%   $103.6259   $103.63   $103.65   $103.60  
  Purchase #2 $126.41   3.355%   $130.6511   $130.65   $130.65   $130.70  
  Purchase #3 $164.71   5.697%   $174.0935   $174.09   $174.10   $174.10  
  Purchase #4 $108.59   8.465%   $117.7821   $117.78   $117.80   $117.80  
  Purchase #5 $128.84   12.622%   $145.1022   $145.10   $145.10   $145.10  
  Purchase #6 $148.30   3.593%   $153.6284   $153.63   $153.65   $153.60  
  Purchase #7 $221.48   5.834%   $234.4011   $234.40   $234.40   $234.40  
  7 purchase totals = $992.67       $1,059.2843   $1,059.28   $1,059.35   $1,059.30