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 $122.52   11.795%   $136.9712   $136.97   $136.95   $137.00  
  Purchase #2 $56.95   5.514%   $60.0902   $60.09   $60.10   $60.10  
  Purchase #3 $46.89   3.716%   $48.6324   $48.63   $48.65   $48.60  
  Purchase #4 $45.54   5.216%   $47.9154   $47.92   $47.90   $47.90  
  Purchase #5 $88.33   10.115%   $97.2646   $97.26   $97.25   $97.30  
  Purchase #6 $41.56   4.824%   $43.5649   $43.56   $43.55   $43.60  
  Purchase #7 $147.75   8.852%   $160.8288   $160.83   $160.85   $160.80  
  7 purchase totals = $549.54       $595.2675   $595.26   $595.25   $595.30