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 $223.43   13.362%   $253.2847   $253.28   $253.30   $253.30  
  Purchase #2 $43.52   7.331%   $46.7105   $46.71   $46.70   $46.70  
  Purchase #3 $94.35   3.349%   $97.5098   $97.51   $97.50   $97.50  
  Purchase #4 $25.46   6.154%   $27.0268   $27.03   $27.05   $27.00  
  Purchase #5 $145.85   4.652%   $152.6349   $152.63   $152.65   $152.60  
  Purchase #6 $11.25   9.545%   $12.3238   $12.32   $12.30   $12.30  
  Purchase #7 $132.44   3.442%   $136.9986   $137.00   $137.00   $137.00  
  7 purchase totals = $676.30       $726.4891   $726.48   $726.50   $726.40