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 $88.44   8.215%   $95.7053   $95.71   $95.70   $95.70  
  Purchase #2 $51.95   3.261%   $53.6441   $53.64   $53.65   $53.60  
  Purchase #3 $7.49   3.345%   $7.7405   $7.74   $7.75   $7.70  
  Purchase #4 $89.67   4.598%   $93.793   $93.79   $93.80   $93.80  
  Purchase #5 $9.75   6.855%   $10.4184   $10.42   $10.40   $10.40  
  Purchase #6 $221.29   4.294%   $230.7922   $230.79   $230.80   $230.80  
  Purchase #7 $182.68   6.537%   $194.6218   $194.62   $194.60   $194.60  
  7 purchase totals = $651.27       $686.7153   $686.71   $686.70   $686.60