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 $23.36   4.827%   $24.4876   $24.49   $24.50   $24.50  
  Purchase #2 $218.96   11.713%   $244.6068   $244.61   $244.60   $244.60  
  Purchase #3 $207.42   10.572%   $229.3484   $229.35   $229.35   $229.30  
  Purchase #4 $161.42   11.832%   $180.5192   $180.52   $180.50   $180.50  
  Purchase #5 $215.64   11.603%   $240.6607   $240.66   $240.65   $240.70  
  Purchase #6 $246.52   9.714%   $270.467   $270.47   $270.45   $270.50  
  Purchase #7 $155.53   3.497%   $160.9689   $160.97   $160.95   $161.00  
  7 purchase totals = $1,228.85       $1,351.0586   $1,351.07   $1,351.00   $1,351.10