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 $181.64   9.296%   $198.5253   $198.53   $198.55   $198.50  
  Purchase #2 $247.52   11.818%   $276.7719   $276.77   $276.75   $276.80  
  Purchase #3 $161.43   4.269%   $168.3214   $168.32   $168.30   $168.30  
  Purchase #4 $112.95   10.606%   $124.9295   $124.93   $124.95   $124.90  
  Purchase #5 $123.30   13.156%   $139.5213   $139.52   $139.50   $139.50  
  Purchase #6 $113.98   5.565%   $120.323   $120.32   $120.30   $120.30  
  Purchase #7 $239.68   11.760%   $267.8664   $267.87   $267.85   $267.90  
  7 purchase totals = $1,180.50       $1,296.2588   $1,296.26   $1,296.20   $1,296.20