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 $29.81   10.280%   $32.8745   $32.87   $32.85   $32.90  
  Purchase #2 $163.95   12.492%   $184.4306   $184.43   $184.45   $184.40  
  Purchase #3 $238.94   3.770%   $247.948   $247.95   $247.95   $247.90  
  Purchase #4 $226.51   12.605%   $255.0616   $255.06   $255.05   $255.10  
  Purchase #5 $227.69   10.865%   $252.4285   $252.43   $252.45   $252.40  
  Purchase #6 $221.80   13.520%   $251.7874   $251.79   $251.80   $251.80  
  Purchase #7 $194.51   3.366%   $201.0572   $201.06   $201.05   $201.10  
  7 purchase totals = $1,303.21       $1,425.5878   $1,425.59   $1,425.60   $1,425.60