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 $191.95   8.239%   $207.7648   $207.76   $207.75   $207.80  
  Purchase #2 $233.45   3.352%   $241.2752   $241.28   $241.30   $241.30  
  Purchase #3 $201.97   8.275%   $218.683   $218.68   $218.70   $218.70  
  Purchase #4 $94.95   6.182%   $100.8198   $100.82   $100.80   $100.80  
  Purchase #5 $217.55   13.571%   $247.0737   $247.07   $247.05   $247.10  
  Purchase #6 $203.26   4.824%   $213.0653   $213.07   $213.05   $213.10  
  Purchase #7 $39.42   5.609%   $41.6311   $41.63   $41.65   $41.60  
  7 purchase totals = $1,182.55       $1,270.3129   $1,270.31   $1,270.30   $1,270.40