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 $96.25   11.190%   $107.0204   $107.02   $107.00   $107.00  
  Purchase #2 $45.97   8.497%   $49.8761   $49.88   $49.90   $49.90  
  Purchase #3 $226.99   10.479%   $250.7763   $250.78   $250.80   $250.80  
  Purchase #4 $68.64   5.461%   $72.3884   $72.39   $72.40   $72.40  
  Purchase #5 $247.70   9.193%   $270.4711   $270.47   $270.45   $270.50  
  Purchase #6 $10.32   12.323%   $11.5917   $11.59   $11.60   $11.60  
  Purchase #7 $242.74   6.672%   $258.9356   $258.94   $258.95   $258.90  
  7 purchase totals = $938.61       $1,021.0596   $1,021.07   $1,021.10   $1,021.10