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 $58.83   11.544%   $65.6213   $65.62   $65.60   $65.60  
  Purchase #2 $26.39   12.839%   $29.7782   $29.78   $29.80   $29.80  
  Purchase #3 $207.40   12.470%   $233.2628   $233.26   $233.25   $233.30  
  Purchase #4 $241.78   5.676%   $255.5034   $255.50   $255.50   $255.50  
  Purchase #5 $53.51   4.678%   $56.0132   $56.01   $56.00   $56.00  
  Purchase #6 $90.56   8.300%   $98.0765   $98.08   $98.10   $98.10  
  Purchase #7 $203.67   13.110%   $230.3711   $230.37   $230.35   $230.40  
  7 purchase totals = $882.14       $968.6265   $968.62   $968.60   $968.70