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 $23.74   6.731%   $25.3379   $25.34   $25.35   $25.30  
  Purchase #2 $238.42   11.841%   $266.6513   $266.65   $266.65   $266.70  
  Purchase #3 $68.64   9.281%   $75.0105   $75.01   $75.00   $75.00  
  Purchase #4 $127.80   8.812%   $139.0617   $139.06   $139.05   $139.10  
  Purchase #5 $8.76   4.296%   $9.1363   $9.14   $9.15   $9.10  
  Purchase #6 $93.85   4.683%   $98.245   $98.25   $98.25   $98.20  
  Purchase #7 $163.64   3.486%   $169.3445   $169.34   $169.35   $169.30  
  7 purchase totals = $724.85       $782.7872   $782.79   $782.80   $782.70