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 $29.81   10.844%   $33.0426   $33.04   $33.05   $33.00  
  Purchase #2 $140.92   4.840%   $147.7405   $147.74   $147.75   $147.70  
  Purchase #3 $58.25   4.268%   $60.7361   $60.74   $60.75   $60.70  
  Purchase #4 $39.44   7.516%   $42.4043   $42.40   $42.40   $42.40  
  Purchase #5 $245.80   7.832%   $265.0511   $265.05   $265.05   $265.10  
  Purchase #6 $181.81   13.176%   $205.7653   $205.77   $205.75   $205.80  
  Purchase #7 $97.44   5.197%   $102.504   $102.50   $102.50   $102.50  
  7 purchase totals = $793.47       $857.2439   $857.24   $857.25   $857.20