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 $56.51   7.167%   $60.5601   $60.56   $60.55   $60.60  
  Purchase #2 $96.78   5.639%   $102.2374   $102.24   $102.25   $102.20  
  Purchase #3 $241.25   6.625%   $257.2328   $257.23   $257.25   $257.20  
  Purchase #4 $87.88   4.537%   $91.8671   $91.87   $91.85   $91.90  
  Purchase #5 $62.33   11.439%   $69.4599   $69.46   $69.45   $69.50  
  Purchase #6 $123.25   3.193%   $127.1854   $127.19   $127.20   $127.20  
  Purchase #7 $93.47   4.831%   $97.9855   $97.99   $98.00   $98.00  
  7 purchase totals = $761.47       $806.5282   $806.54   $806.55   $806.60