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 $138.29   13.845%   $157.4363   $157.44   $157.45   $157.40  
  Purchase #2 $173.70   7.272%   $186.3315   $186.33   $186.35   $186.30  
  Purchase #3 $31.96   8.214%   $34.5852   $34.59   $34.60   $34.60  
  Purchase #4 $157.45   7.669%   $169.5248   $169.52   $169.50   $169.50  
  Purchase #5 $154.74   11.318%   $172.2535   $172.25   $172.25   $172.30  
  Purchase #6 $59.37   4.274%   $61.9075   $61.91   $61.90   $61.90  
  Purchase #7 $5.72   13.229%   $6.4767   $6.48   $6.50   $6.50  
  7 purchase totals = $721.23       $788.5155   $788.52   $788.55   $788.50