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 $68.27   9.138%   $74.5085   $74.51   $74.50   $74.50  
  Purchase #2 $128.48   13.203%   $145.4432   $145.44   $145.45   $145.40  
  Purchase #3 $143.89   3.397%   $148.7779   $148.78   $148.80   $148.80  
  Purchase #4 $207.36   6.378%   $220.5854   $220.59   $220.60   $220.60  
  Purchase #5 $157.55   12.277%   $176.8924   $176.89   $176.90   $176.90  
  Purchase #6 $127.82   5.611%   $134.992   $134.99   $135.00   $135.00  
  Purchase #7 $43.88   11.289%   $48.8336   $48.83   $48.85   $48.80  
  7 purchase totals = $877.25       $950.0330   $950.03   $950.10   $950.00