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 $223.79   11.547%   $249.631   $249.63   $249.65   $249.60  
  Purchase #2 $44.41   8.649%   $48.251   $48.25   $48.25   $48.30  
  Purchase #3 $150.31   12.267%   $168.7485   $168.75   $168.75   $168.70  
  Purchase #4 $245.60   4.330%   $256.2345   $256.23   $256.25   $256.20  
  Purchase #5 $46.38   6.646%   $49.4624   $49.46   $49.45   $49.50  
  Purchase #6 $239.36   8.141%   $258.8463   $258.85   $258.85   $258.80  
  Purchase #7 $147.43   3.803%   $153.0368   $153.04   $153.05   $153.00  
  7 purchase totals = $1,097.28       $1,184.2105   $1,184.21   $1,184.25   $1,184.10