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 $59.53   12.351%   $66.8826   $66.88   $66.90   $66.90  
  Purchase #2 $172.94   12.664%   $194.8411   $194.84   $194.85   $194.80  
  Purchase #3 $109.52   3.264%   $113.0947   $113.09   $113.10   $113.10  
  Purchase #4 $37.73   6.127%   $40.0417   $40.04   $40.05   $40.00  
  Purchase #5 $112.35   7.538%   $120.8189   $120.82   $120.80   $120.80  
  Purchase #6 $32.66   5.509%   $34.4592   $34.46   $34.45   $34.50  
  Purchase #7 $128.38   9.764%   $140.915   $140.92   $140.90   $140.90  
  7 purchase totals = $653.11       $711.0532   $711.05   $711.05   $711.00