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 $32.64   6.346%   $34.7113   $34.71   $34.70   $34.70  
  Purchase #2 $197.58   3.556%   $204.6059   $204.61   $204.60   $204.60  
  Purchase #3 $190.65   10.102%   $209.9095   $209.91   $209.90   $209.90  
  Purchase #4 $40.93   12.351%   $45.9853   $45.99   $46.00   $46.00  
  Purchase #5 $134.34   6.764%   $143.4268   $143.43   $143.45   $143.40  
  Purchase #6 $77.31   6.187%   $82.0932   $82.09   $82.10   $82.10  
  Purchase #7 $192.51   7.786%   $207.4988   $207.50   $207.50   $207.50  
  7 purchase totals = $865.96       $928.2308   $928.24   $928.25   $928.20