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 $85.26   12.832%   $96.2006   $96.20   $96.20   $96.20  
  Purchase #2 $186.55   7.718%   $200.9479   $200.95   $200.95   $200.90  
  Purchase #3 $24.94   12.150%   $27.9702   $27.97   $27.95   $28.00  
  Purchase #4 $17.69   4.805%   $18.54   $18.54   $18.55   $18.50  
  Purchase #5 $80.54   9.802%   $88.4345   $88.43   $88.45   $88.40  
  Purchase #6 $174.33   11.505%   $194.3867   $194.39   $194.40   $194.40  
  Purchase #7 $44.65   12.351%   $50.1647   $50.16   $50.15   $50.20  
  7 purchase totals = $613.96       $676.6446   $676.64   $676.65   $676.60