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 $49.47   6.267%   $52.5703   $52.57   $52.55   $52.60  
  Purchase #2 $94.91   7.797%   $102.3101   $102.31   $102.30   $102.30  
  Purchase #3 $51.85   9.752%   $56.9064   $56.91   $56.90   $56.90  
  Purchase #4 $141.49   10.595%   $156.4809   $156.48   $156.50   $156.50  
  Purchase #5 $184.28   12.394%   $207.1197   $207.12   $207.10   $207.10  
  Purchase #6 $249.65   5.680%   $263.8301   $263.83   $263.85   $263.80  
  Purchase #7 $174.80   9.577%   $191.5406   $191.54   $191.55   $191.50  
  7 purchase totals = $946.45       $1,030.7581   $1,030.76   $1,030.75   $1,030.70