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 $24.57   5.121%   $25.8282   $25.83   $25.85   $25.80  
  Purchase #2 $23.84   4.193%   $24.8396   $24.84   $24.85   $24.80  
  Purchase #3 $219.28   6.795%   $234.1801   $234.18   $234.20   $234.20  
  Purchase #4 $86.95   9.616%   $95.3111   $95.31   $95.30   $95.30  
  Purchase #5 $144.98   12.332%   $162.8589   $162.86   $162.85   $162.90  
  Purchase #6 $67.52   11.684%   $75.409   $75.41   $75.40   $75.40  
  Purchase #7 $163.38   11.721%   $182.5298   $182.53   $182.55   $182.50  
  7 purchase totals = $730.52       $800.9567   $800.96   $801.00   $800.90