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 $55.77   7.173%   $59.7704   $59.77   $59.75   $59.80  
  Purchase #2 $118.64   11.815%   $132.6573   $132.66   $132.65   $132.70  
  Purchase #3 $40.93   13.653%   $46.5182   $46.52   $46.50   $46.50  
  Purchase #4 $72.55   4.611%   $75.8953   $75.90   $75.90   $75.90  
  Purchase #5 $206.85   11.789%   $231.2355   $231.24   $231.25   $231.20  
  Purchase #6 $185.40   9.260%   $202.568   $202.57   $202.55   $202.60  
  Purchase #7 $221.59   9.585%   $242.8294   $242.83   $242.85   $242.80  
  7 purchase totals = $901.73       $991.4741   $991.49   $991.45   $991.50