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 $155.64   13.512%   $176.6701   $176.67   $176.65   $176.70  
  Purchase #2 $189.82   13.313%   $215.0907   $215.09   $215.10   $215.10  
  Purchase #3 $5.30   12.178%   $5.9454   $5.95   $5.95   $5.90  
  Purchase #4 $57.52   7.472%   $61.8179   $61.82   $61.80   $61.80  
  Purchase #5 $42.48   9.589%   $46.5534   $46.55   $46.55   $46.60  
  Purchase #6 $233.83   11.427%   $260.5498   $260.55   $260.55   $260.50  
  Purchase #7 $247.28   3.259%   $255.3389   $255.34   $255.35   $255.30  
  7 purchase totals = $931.87       $1,021.9662   $1,021.97   $1,021.95   $1,021.90