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 $161.65   11.139%   $179.6562   $179.66   $179.65   $179.70  
  Purchase #2 $143.99   8.280%   $155.9124   $155.91   $155.90   $155.90  
  Purchase #3 $107.29   7.340%   $115.1651   $115.17   $115.15   $115.20  
  Purchase #4 $177.46   9.463%   $194.253   $194.25   $194.25   $194.30  
  Purchase #5 $229.72   7.468%   $246.8755   $246.88   $246.90   $246.90  
  Purchase #6 $39.99   3.279%   $41.3013   $41.30   $41.30   $41.30  
  Purchase #7 $60.87   12.264%   $68.3351   $68.34   $68.35   $68.30  
  7 purchase totals = $920.97       $1,001.4986   $1,001.51   $1,001.50   $1,001.60