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 $64.50   6.194%   $68.4951   $68.50   $68.50   $68.50  
  Purchase #2 $228.87   6.372%   $243.4536   $243.45   $243.45   $243.50  
  Purchase #3 $171.40   9.298%   $187.3368   $187.34   $187.35   $187.30  
  Purchase #4 $212.88   4.511%   $222.483   $222.48   $222.50   $222.50  
  Purchase #5 $166.49   10.149%   $183.3871   $183.39   $183.40   $183.40  
  Purchase #6 $137.85   10.226%   $151.9465   $151.95   $151.95   $151.90  
  Purchase #7 $206.41   4.121%   $214.9162   $214.92   $214.90   $214.90  
  7 purchase totals = $1,188.40       $1,272.0183   $1,272.03   $1,272.05   $1,272.00