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 $58.32   4.613%   $61.0103   $61.01   $61.00   $61.00  
  Purchase #2 $138.44   5.223%   $145.6707   $145.67   $145.65   $145.70  
  Purchase #3 $230.67   5.122%   $242.4849   $242.48   $242.50   $242.50  
  Purchase #4 $111.63   9.356%   $122.0741   $122.07   $122.05   $122.10  
  Purchase #5 $24.90   7.470%   $26.76   $26.76   $26.75   $26.80  
  Purchase #6 $119.58   11.828%   $133.7239   $133.72   $133.70   $133.70  
  Purchase #7 $10.40   8.263%   $11.2594   $11.26   $11.25   $11.30  
  7 purchase totals = $693.94       $742.9833   $742.97   $742.90   $743.10