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 $53.53   5.824%   $56.6476   $56.65   $56.65   $56.60  
  Purchase #2 $191.81   7.220%   $205.6587   $205.66   $205.65   $205.70  
  Purchase #3 $233.92   5.824%   $247.5435   $247.54   $247.55   $247.50  
  Purchase #4 $109.97   11.824%   $122.9729   $122.97   $122.95   $123.00  
  Purchase #5 $178.61   12.366%   $200.6969   $200.70   $200.70   $200.70  
  Purchase #6 $42.58   12.645%   $47.9642   $47.96   $47.95   $48.00  
  Purchase #7 $15.58   4.447%   $16.2728   $16.27   $16.25   $16.30  
  7 purchase totals = $826.00       $897.7566   $897.75   $897.70   $897.80