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 $50.84   9.627%   $55.7344   $55.73   $55.75   $55.70  
  Purchase #2 $235.49   13.593%   $267.5002   $267.50   $267.50   $267.50  
  Purchase #3 $232.43   6.467%   $247.4612   $247.46   $247.45   $247.50  
  Purchase #4 $196.85   7.792%   $212.1886   $212.19   $212.20   $212.20  
  Purchase #5 $69.67   6.350%   $74.094   $74.09   $74.10   $74.10  
  Purchase #6 $234.36   3.801%   $243.268   $243.27   $243.25   $243.30  
  Purchase #7 $76.76   6.443%   $81.7056   $81.71   $81.70   $81.70  
  7 purchase totals = $1,096.40       $1,181.9520   $1,181.95   $1,181.95   $1,182.00