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 $168.85   5.626%   $178.3495   $178.35   $178.35   $178.30  
  Purchase #2 $245.79   9.425%   $268.9557   $268.96   $268.95   $269.00  
  Purchase #3 $65.30   8.349%   $70.7519   $70.75   $70.75   $70.80  
  Purchase #4 $60.95   7.662%   $65.62   $65.62   $65.60   $65.60  
  Purchase #5 $55.51   13.590%   $63.0538   $63.05   $63.05   $63.10  
  Purchase #6 $199.25   3.671%   $206.5645   $206.56   $206.55   $206.60  
  Purchase #7 $21.40   11.543%   $23.8702   $23.87   $23.85   $23.90  
  7 purchase totals = $817.05       $877.1656   $877.16   $877.10   $877.30