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 $56.53   9.557%   $61.9326   $61.93   $61.95   $61.90  
  Purchase #2 $126.48   4.805%   $132.5574   $132.56   $132.55   $132.60  
  Purchase #3 $98.90   8.812%   $107.6151   $107.62   $107.60   $107.60  
  Purchase #4 $8.57   10.263%   $9.4495   $9.45   $9.45   $9.40  
  Purchase #5 $109.97   6.169%   $116.754   $116.75   $116.75   $116.80  
  Purchase #6 $194.61   9.616%   $213.3237   $213.32   $213.30   $213.30  
  Purchase #7 $50.42   6.722%   $53.8092   $53.81   $53.80   $53.80  
  7 purchase totals = $645.48       $695.4415   $695.44   $695.40   $695.40