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 $110.52   11.255%   $122.959   $122.96   $122.95   $123.00  
  Purchase #2 $103.87   6.658%   $110.7857   $110.79   $110.80   $110.80  
  Purchase #3 $230.68   7.811%   $248.6984   $248.70   $248.70   $248.70  
  Purchase #4 $127.86   5.285%   $134.6174   $134.62   $134.60   $134.60  
  Purchase #5 $113.65   9.769%   $124.7525   $124.75   $124.75   $124.80  
  Purchase #6 $244.87   9.393%   $267.8706   $267.87   $267.85   $267.90  
  Purchase #7 $222.42   5.182%   $233.9458   $233.95   $233.95   $233.90  
  7 purchase totals = $1,153.87       $1,243.6294   $1,243.64   $1,243.60   $1,243.70