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 $24.69   7.413%   $26.5203   $26.52   $26.50   $26.50  
  Purchase #2 $245.81   13.113%   $278.0431   $278.04   $278.05   $278.00  
  Purchase #3 $45.74   13.438%   $51.8865   $51.89   $51.90   $51.90  
  Purchase #4 $201.98   9.481%   $221.1297   $221.13   $221.15   $221.10  
  Purchase #5 $62.26   9.131%   $67.945   $67.95   $67.95   $67.90  
  Purchase #6 $222.74   8.558%   $241.8021   $241.80   $241.80   $241.80  
  Purchase #7 $58.85   11.272%   $65.4836   $65.48   $65.50   $65.50  
  7 purchase totals = $862.07       $952.8103   $952.81   $952.85   $952.70