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 $233.78   10.472%   $258.2614   $258.26   $258.25   $258.30  
  Purchase #2 $160.61   11.720%   $179.4335   $179.43   $179.45   $179.40  
  Purchase #3 $20.85   12.516%   $23.4596   $23.46   $23.45   $23.50  
  Purchase #4 $123.98   10.718%   $137.2682   $137.27   $137.25   $137.30  
  Purchase #5 $158.62   8.834%   $172.6325   $172.63   $172.65   $172.60  
  Purchase #6 $165.79   5.616%   $175.1008   $175.10   $175.10   $175.10  
  Purchase #7 $17.80   9.123%   $19.4239   $19.42   $19.40   $19.40  
  7 purchase totals = $881.43       $965.5799   $965.57   $965.55   $965.60