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 $237.85   10.752%   $263.4236   $263.42   $263.40   $263.40  
  Purchase #2 $34.92   3.501%   $36.1425   $36.14   $36.15   $36.10  
  Purchase #3 $37.77   3.136%   $38.9545   $38.95   $38.95   $39.00  
  Purchase #4 $87.45   8.139%   $94.5676   $94.57   $94.55   $94.60  
  Purchase #5 $5.45   12.190%   $6.1144   $6.11   $6.10   $6.10  
  Purchase #6 $214.98   8.505%   $233.264   $233.26   $233.25   $233.30  
  Purchase #7 $54.93   13.801%   $62.5109   $62.51   $62.50   $62.50  
  7 purchase totals = $673.35       $734.9775   $734.96   $734.90   $735.00