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 $126.52   7.222%   $135.6573   $135.66   $135.65   $135.70  
  Purchase #2 $249.55   11.255%   $277.6369   $277.64   $277.65   $277.60  
  Purchase #3 $173.44   8.115%   $187.5147   $187.51   $187.50   $187.50  
  Purchase #4 $48.68   13.531%   $55.2669   $55.27   $55.25   $55.30  
  Purchase #5 $102.74   10.133%   $113.1506   $113.15   $113.15   $113.20  
  Purchase #6 $90.42   6.756%   $96.5288   $96.53   $96.55   $96.50  
  Purchase #7 $73.62   4.442%   $76.8902   $76.89   $76.90   $76.90  
  7 purchase totals = $864.97       $942.6454   $942.65   $942.65   $942.70