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 $32.77   10.420%   $36.1846   $36.18   $36.20   $36.20  
  Purchase #2 $234.67   5.225%   $246.9315   $246.93   $246.95   $246.90  
  Purchase #3 $234.44   13.119%   $265.1962   $265.20   $265.20   $265.20  
  Purchase #4 $199.90   12.689%   $225.2653   $225.27   $225.25   $225.30  
  Purchase #5 $45.41   4.738%   $47.5615   $47.56   $47.55   $47.60  
  Purchase #6 $214.61   13.563%   $243.7176   $243.72   $243.70   $243.70  
  Purchase #7 $29.32   4.373%   $30.6022   $30.60   $30.60   $30.60  
  7 purchase totals = $991.12       $1,095.4589   $1,095.46   $1,095.45   $1,095.50