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 $34.83   3.458%   $36.0344   $36.03   $36.05   $36.00  
  Purchase #2 $68.33   8.798%   $74.3417   $74.34   $74.35   $74.30  
  Purchase #3 $91.43   12.168%   $102.5552   $102.56   $102.55   $102.60  
  Purchase #4 $58.58   12.478%   $65.8896   $65.89   $65.90   $65.90  
  Purchase #5 $126.53   8.560%   $137.361   $137.36   $137.35   $137.40  
  Purchase #6 $96.93   9.315%   $105.959   $105.96   $105.95   $106.00  
  Purchase #7 $179.30   4.633%   $187.607   $187.61   $187.60   $187.60  
  7 purchase totals = $655.93       $709.7479   $709.75   $709.75   $709.80