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 $155.64   13.741%   $177.0265   $177.03   $177.05   $177.00  
  Purchase #2 $130.36   8.247%   $141.1108   $141.11   $141.10   $141.10  
  Purchase #3 $245.86   4.764%   $257.5728   $257.57   $257.55   $257.60  
  Purchase #4 $48.61   10.394%   $53.6625   $53.66   $53.65   $53.70  
  Purchase #5 $23.85   12.818%   $26.9071   $26.91   $26.90   $26.90  
  Purchase #6 $93.74   13.303%   $106.2102   $106.21   $106.20   $106.20  
  Purchase #7 $240.42   12.266%   $269.9099   $269.91   $269.90   $269.90  
  7 purchase totals = $938.48       $1,032.3998   $1,032.40   $1,032.35   $1,032.40