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 $72.61   13.344%   $82.2991   $82.30   $82.30   $82.30  
  Purchase #2 $233.85   8.157%   $252.9251   $252.93   $252.95   $252.90  
  Purchase #3 $201.27   11.656%   $224.73   $224.73   $224.75   $224.70  
  Purchase #4 $192.57   3.743%   $199.7779   $199.78   $199.80   $199.80  
  Purchase #5 $147.57   8.291%   $159.805   $159.81   $159.80   $159.80  
  Purchase #6 $140.54   7.103%   $150.5226   $150.52   $150.50   $150.50  
  Purchase #7 $27.62   3.585%   $28.6102   $28.61   $28.60   $28.60  
  7 purchase totals = $1,016.03       $1,098.6699   $1,098.68   $1,098.70   $1,098.60