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 $136.46   13.266%   $154.5628   $154.56   $154.55   $154.60  
  Purchase #2 $113.97   4.133%   $118.6804   $118.68   $118.70   $118.70  
  Purchase #3 $250.71   5.523%   $264.5567   $264.56   $264.55   $264.60  
  Purchase #4 $119.99   6.446%   $127.7246   $127.72   $127.70   $127.70  
  Purchase #5 $204.35   7.624%   $219.9296   $219.93   $219.95   $219.90  
  Purchase #6 $116.41   4.269%   $121.3795   $121.38   $121.40   $121.40  
  Purchase #7 $107.60   10.403%   $118.7936   $118.79   $118.80   $118.80  
  7 purchase totals = $1,049.49       $1,125.6272   $1,125.62   $1,125.65   $1,125.70