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 $180.50   12.314%   $202.7268   $202.73   $202.75   $202.70  
  Purchase #2 $107.68   10.579%   $119.0715   $119.07   $119.05   $119.10  
  Purchase #3 $56.31   11.483%   $62.7761   $62.78   $62.80   $62.80  
  Purchase #4 $119.72   11.474%   $133.4567   $133.46   $133.45   $133.50  
  Purchase #5 $183.85   7.767%   $198.1296   $198.13   $198.15   $198.10  
  Purchase #6 $123.63   12.696%   $139.3261   $139.33   $139.35   $139.30  
  Purchase #7 $147.55   13.541%   $167.5297   $167.53   $167.55   $167.50  
  7 purchase totals = $919.24       $1,023.0165   $1,023.03   $1,023.10   $1,023.00