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 $214.93   8.123%   $232.3888   $232.39   $232.40   $232.40  
  Purchase #2 $194.37   6.649%   $207.2937   $207.29   $207.30   $207.30  
  Purchase #3 $89.95   6.176%   $95.5053   $95.51   $95.50   $95.50  
  Purchase #4 $215.80   8.586%   $234.3286   $234.33   $234.35   $234.30  
  Purchase #5 $185.40   11.531%   $206.7785   $206.78   $206.80   $206.80  
  Purchase #6 $235.50   8.417%   $255.322   $255.32   $255.30   $255.30  
  Purchase #7 $100.57   5.678%   $106.2804   $106.28   $106.30   $106.30  
  7 purchase totals = $1,236.52       $1,337.8973   $1,337.90   $1,337.95   $1,337.90