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 $52.77   13.618%   $59.9562   $59.96   $59.95   $60.00  
  Purchase #2 $196.74   6.748%   $210.016   $210.02   $210.00   $210.00  
  Purchase #3 $221.96   7.149%   $237.8279   $237.83   $237.85   $237.80  
  Purchase #4 $161.59   8.138%   $174.7402   $174.74   $174.75   $174.70  
  Purchase #5 $148.73   4.161%   $154.9187   $154.92   $154.90   $154.90  
  Purchase #6 $166.68   10.411%   $184.0331   $184.03   $184.05   $184.00  
  Purchase #7 $17.47   6.819%   $18.6613   $18.66   $18.65   $18.70  
  7 purchase totals = $965.94       $1,040.1534   $1,040.16   $1,040.15   $1,040.10