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 $46.29   3.134%   $47.7407   $47.74   $47.75   $47.70  
  Purchase #2 $210.66   4.686%   $220.5315   $220.53   $220.55   $220.50  
  Purchase #3 $208.48   5.721%   $220.4071   $220.41   $220.40   $220.40  
  Purchase #4 $32.85   8.309%   $35.5795   $35.58   $35.60   $35.60  
  Purchase #5 $194.50   3.620%   $201.5409   $201.54   $201.55   $201.50  
  Purchase #6 $125.97   7.263%   $135.1192   $135.12   $135.10   $135.10  
  Purchase #7 $167.34   12.604%   $188.4315   $188.43   $188.45   $188.40  
  7 purchase totals = $986.09       $1,049.3504   $1,049.35   $1,049.40   $1,049.20