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 $216.84   5.849%   $229.523   $229.52   $229.50   $229.50  
  Purchase #2 $13.78   3.284%   $14.2325   $14.23   $14.25   $14.20  
  Purchase #3 $53.99   8.332%   $58.4884   $58.49   $58.50   $58.50  
  Purchase #4 $219.41   3.370%   $226.8041   $226.80   $226.80   $226.80  
  Purchase #5 $112.82   5.197%   $118.6833   $118.68   $118.70   $118.70  
  Purchase #6 $241.33   8.524%   $261.901   $261.90   $261.90   $261.90  
  Purchase #7 $72.58   12.235%   $81.4602   $81.46   $81.45   $81.50  
  7 purchase totals = $930.75       $991.0925   $991.08   $991.10   $991.10