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 $67.58   9.377%   $73.917   $73.92   $73.90   $73.90  
  Purchase #2 $11.56   9.452%   $12.6527   $12.65   $12.65   $12.70  
  Purchase #3 $167.69   4.207%   $174.7447   $174.74   $174.75   $174.70  
  Purchase #4 $12.53   7.751%   $13.5012   $13.50   $13.50   $13.50  
  Purchase #5 $92.64   5.623%   $97.8491   $97.85   $97.85   $97.80  
  Purchase #6 $203.35   4.540%   $212.5821   $212.58   $212.60   $212.60  
  Purchase #7 $146.73   4.533%   $153.3813   $153.38   $153.40   $153.40  
  7 purchase totals = $702.08       $738.6281   $738.62   $738.65   $738.60