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 $233.57   9.473%   $255.6961   $255.70   $255.70   $255.70  
  Purchase #2 $52.75   13.651%   $59.9509   $59.95   $59.95   $60.00  
  Purchase #3 $158.73   9.536%   $173.8665   $173.87   $173.85   $173.90  
  Purchase #4 $219.39   13.494%   $248.9945   $248.99   $249.00   $249.00  
  Purchase #5 $174.38   11.231%   $193.9646   $193.96   $193.95   $194.00  
  Purchase #6 $204.77   9.799%   $224.8354   $224.84   $224.85   $224.80  
  Purchase #7 $238.43   3.494%   $246.7607   $246.76   $246.75   $246.80  
  7 purchase totals = $1,282.02       $1,404.0687   $1,404.07   $1,404.05   $1,404.20