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 $138.84   3.846%   $144.1798   $144.18   $144.20   $144.20  
  Purchase #2 $122.45   5.443%   $129.115   $129.12   $129.10   $129.10  
  Purchase #3 $203.46   5.288%   $214.219   $214.22   $214.20   $214.20  
  Purchase #4 $17.38   3.786%   $18.038   $18.04   $18.05   $18.00  
  Purchase #5 $137.30   8.465%   $148.9224   $148.92   $148.90   $148.90  
  Purchase #6 $43.64   7.573%   $46.9449   $46.94   $46.95   $46.90  
  Purchase #7 $124.92   3.481%   $129.2685   $129.27   $129.25   $129.30  
  7 purchase totals = $787.99       $830.6876   $830.69   $830.65   $830.60