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 $246.93   8.243%   $267.2844   $267.28   $267.30   $267.30  
  Purchase #2 $68.37   6.580%   $72.8687   $72.87   $72.85   $72.90  
  Purchase #3 $172.65   3.705%   $179.0467   $179.05   $179.05   $179.00  
  Purchase #4 $196.80   13.246%   $222.8681   $222.87   $222.85   $222.90  
  Purchase #5 $226.27   7.804%   $243.9281   $243.93   $243.95   $243.90  
  Purchase #6 $193.88   5.612%   $204.7605   $204.76   $204.75   $204.80  
  Purchase #7 $11.30   3.727%   $11.7212   $11.72   $11.70   $11.70  
  7 purchase totals = $1,116.20       $1,202.4777   $1,202.48   $1,202.45   $1,202.50