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 $25.73   3.315%   $26.5829   $26.58   $26.60   $26.60  
  Purchase #2 $10.55   4.780%   $11.0543   $11.05   $11.05   $11.10  
  Purchase #3 $132.76   5.837%   $140.5092   $140.51   $140.50   $140.50  
  Purchase #4 $225.61   13.747%   $256.6246   $256.62   $256.60   $256.60  
  Purchase #5 $37.80   8.851%   $41.1457   $41.15   $41.15   $41.10  
  Purchase #6 $123.87   13.585%   $140.6977   $140.70   $140.70   $140.70  
  Purchase #7 $79.29   8.743%   $86.2223   $86.22   $86.20   $86.20  
  7 purchase totals = $635.61       $702.8367   $702.83   $702.80   $702.80