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 $82.78   11.423%   $92.236   $92.24   $92.25   $92.20  
  Purchase #2 $184.83   8.182%   $199.9528   $199.95   $199.95   $200.00  
  Purchase #3 $245.64   4.396%   $256.4383   $256.44   $256.45   $256.40  
  Purchase #4 $219.39   6.685%   $234.0562   $234.06   $234.05   $234.10  
  Purchase #5 $16.46   6.294%   $17.496   $17.50   $17.50   $17.50  
  Purchase #6 $239.60   5.661%   $253.1638   $253.16   $253.15   $253.20  
  Purchase #7 $126.85   6.206%   $134.7223   $134.72   $134.70   $134.70  
  7 purchase totals = $1,115.55       $1,188.0654   $1,188.07   $1,188.05   $1,188.10