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 $204.59   13.655%   $232.5268   $232.53   $232.55   $232.50  
  Purchase #2 $91.45   5.687%   $96.6508   $96.65   $96.65   $96.70  
  Purchase #3 $83.86   3.587%   $86.8681   $86.87   $86.85   $86.90  
  Purchase #4 $147.59   4.536%   $154.2847   $154.28   $154.30   $154.30  
  Purchase #5 $216.27   4.846%   $226.7504   $226.75   $226.75   $226.80  
  Purchase #6 $132.52   8.304%   $143.5245   $143.52   $143.50   $143.50  
  Purchase #7 $41.27   13.510%   $46.8456   $46.85   $46.85   $46.80  
  7 purchase totals = $917.55       $987.4509   $987.45   $987.45   $987.50