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 $66.40   11.207%   $73.8414   $73.84   $73.85   $73.80  
  Purchase #2 $171.96   8.498%   $186.5732   $186.57   $186.55   $186.60  
  Purchase #3 $248.63   7.681%   $267.7273   $267.73   $267.75   $267.70  
  Purchase #4 $219.82   8.640%   $238.8124   $238.81   $238.80   $238.80  
  Purchase #5 $221.42   10.559%   $244.7997   $244.80   $244.80   $244.80  
  Purchase #6 $162.79   7.785%   $175.4632   $175.46   $175.45   $175.50  
  Purchase #7 $93.75   4.736%   $98.19   $98.19   $98.20   $98.20  
  7 purchase totals = $1,184.77       $1,285.4072   $1,285.40   $1,285.40   $1,285.40