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 $63.83   9.603%   $69.9596   $69.96   $69.95   $70.00  
  Purchase #2 $228.93   6.489%   $243.7853   $243.79   $243.80   $243.80  
  Purchase #3 $25.99   11.327%   $28.9339   $28.93   $28.95   $28.90  
  Purchase #4 $82.42   13.414%   $93.4758   $93.48   $93.50   $93.50  
  Purchase #5 $237.98   10.129%   $262.085   $262.09   $262.10   $262.10  
  Purchase #6 $136.99   5.685%   $144.7779   $144.78   $144.80   $144.80  
  Purchase #7 $192.41   12.738%   $216.9192   $216.92   $216.90   $216.90  
  7 purchase totals = $968.55       $1,059.9367   $1,059.95   $1,060.00   $1,060.00