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 $82.93   3.712%   $86.0084   $86.01   $86.00   $86.00  
  Purchase #2 $117.99   4.638%   $123.4624   $123.46   $123.45   $123.50  
  Purchase #3 $166.64   12.334%   $187.1934   $187.19   $187.20   $187.20  
  Purchase #4 $68.86   9.299%   $75.2633   $75.26   $75.25   $75.30  
  Purchase #5 $203.52   7.651%   $219.0913   $219.09   $219.10   $219.10  
  Purchase #6 $246.48   9.869%   $270.8051   $270.81   $270.80   $270.80  
  Purchase #7 $243.72   9.116%   $265.9375   $265.94   $265.95   $265.90  
  7 purchase totals = $1,130.14       $1,227.7614   $1,227.76   $1,227.75   $1,227.80