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 $203.41   7.178%   $218.0108   $218.01   $218.00   $218.00  
  Purchase #2 $65.98   11.240%   $73.3962   $73.40   $73.40   $73.40  
  Purchase #3 $186.72   3.873%   $193.9517   $193.95   $193.95   $194.00  
  Purchase #4 $111.50   6.422%   $118.6605   $118.66   $118.65   $118.70  
  Purchase #5 $12.50   11.529%   $13.9411   $13.94   $13.95   $13.90  
  Purchase #6 $77.25   13.357%   $87.5683   $87.57   $87.55   $87.60  
  Purchase #7 $80.66   6.329%   $85.765   $85.77   $85.75   $85.80  
  7 purchase totals = $738.02       $791.2936   $791.30   $791.25   $791.40