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 $216.90   7.664%   $233.5232   $233.52   $233.50   $233.50  
  Purchase #2 $151.95   8.607%   $165.0283   $165.03   $165.05   $165.00  
  Purchase #3 $5.90   5.326%   $6.2142   $6.21   $6.20   $6.20  
  Purchase #4 $118.49   6.493%   $126.1836   $126.18   $126.20   $126.20  
  Purchase #5 $107.65   11.467%   $119.9942   $119.99   $120.00   $120.00  
  Purchase #6 $212.40   6.631%   $226.4842   $226.48   $226.50   $226.50  
  Purchase #7 $48.32   6.168%   $51.3004   $51.30   $51.30   $51.30  
  7 purchase totals = $861.61       $928.7281   $928.71   $928.75   $928.70