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 $62.68   3.826%   $65.0781   $65.08   $65.10   $65.10  
  Purchase #2 $213.85   8.803%   $232.6752   $232.68   $232.70   $232.70  
  Purchase #3 $208.55   7.527%   $224.2476   $224.25   $224.25   $224.20  
  Purchase #4 $55.85   9.547%   $61.182   $61.18   $61.20   $61.20  
  Purchase #5 $196.34   4.537%   $205.2479   $205.25   $205.25   $205.20  
  Purchase #6 $218.79   5.556%   $230.946   $230.95   $230.95   $230.90  
  Purchase #7 $122.51   9.725%   $134.4241   $134.42   $134.40   $134.40  
  7 purchase totals = $1,078.57       $1,153.8009   $1,153.81   $1,153.85   $1,153.70