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 $68.71   3.212%   $70.917   $70.92   $70.90   $70.90  
  Purchase #2 $34.26   10.780%   $37.9532   $37.95   $37.95   $38.00  
  Purchase #3 $57.97   13.190%   $65.6162   $65.62   $65.60   $65.60  
  Purchase #4 $240.79   13.758%   $273.9179   $273.92   $273.90   $273.90  
  Purchase #5 $156.89   10.672%   $173.6333   $173.63   $173.65   $173.60  
  Purchase #6 $39.56   3.872%   $41.0918   $41.09   $41.10   $41.10  
  Purchase #7 $249.95   8.337%   $270.7883   $270.79   $270.80   $270.80  
  7 purchase totals = $848.13       $933.9177   $933.92   $933.90   $933.90