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 $244.76   8.412%   $265.3492   $265.35   $265.35   $265.30  
  Purchase #2 $175.39   3.793%   $182.0425   $182.04   $182.05   $182.00  
  Purchase #3 $80.61   7.858%   $86.9443   $86.94   $86.95   $86.90  
  Purchase #4 $171.97   4.530%   $179.7602   $179.76   $179.75   $179.80  
  Purchase #5 $227.83   8.823%   $247.9314   $247.93   $247.95   $247.90  
  Purchase #6 $44.82   4.600%   $46.8817   $46.88   $46.90   $46.90  
  Purchase #7 $150.55   11.645%   $168.0815   $168.08   $168.10   $168.10  
  7 purchase totals = $1,095.93       $1,176.9908   $1,176.98   $1,177.05   $1,176.90