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 $188.99   4.643%   $197.7648   $197.76   $197.75   $197.80  
  Purchase #2 $204.76   8.207%   $221.5647   $221.56   $221.55   $221.60  
  Purchase #3 $63.52   7.466%   $68.2624   $68.26   $68.25   $68.30  
  Purchase #4 $78.81   11.241%   $87.669   $87.67   $87.65   $87.70  
  Purchase #5 $62.54   11.297%   $69.6051   $69.61   $69.60   $69.60  
  Purchase #6 $216.36   7.349%   $232.2603   $232.26   $232.25   $232.30  
  Purchase #7 $81.28   5.769%   $85.969   $85.97   $85.95   $86.00  
  7 purchase totals = $896.26       $963.0953   $963.09   $963.00   $963.30