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 $86.42   11.756%   $96.5795   $96.58   $96.60   $96.60  
  Purchase #2 $178.61   8.240%   $193.3275   $193.33   $193.35   $193.30  
  Purchase #3 $80.97   13.713%   $92.0734   $92.07   $92.05   $92.10  
  Purchase #4 $25.34   5.217%   $26.662   $26.66   $26.65   $26.70  
  Purchase #5 $239.37   5.775%   $253.1936   $253.19   $253.20   $253.20  
  Purchase #6 $16.78   10.744%   $18.5828   $18.58   $18.60   $18.60  
  Purchase #7 $247.30   10.431%   $273.0959   $273.10   $273.10   $273.10  
  7 purchase totals = $874.79       $953.5147   $953.51   $953.55   $953.60