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 $207.69   10.719%   $229.9523   $229.95   $229.95   $230.00  
  Purchase #2 $40.86   6.119%   $43.3602   $43.36   $43.35   $43.40  
  Purchase #3 $225.78   12.745%   $254.5557   $254.56   $254.55   $254.60  
  Purchase #4 $178.26   9.577%   $195.332   $195.33   $195.35   $195.30  
  Purchase #5 $58.32   12.176%   $65.421   $65.42   $65.40   $65.40  
  Purchase #6 $53.78   5.248%   $56.6024   $56.60   $56.60   $56.60  
  Purchase #7 $179.33   10.189%   $197.6019   $197.60   $197.60   $197.60  
  7 purchase totals = $944.02       $1,042.8255   $1,042.82   $1,042.80   $1,042.90