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 $184.35   4.618%   $192.8633   $192.86   $192.85   $192.90  
  Purchase #2 $127.46   4.555%   $133.2658   $133.27   $133.25   $133.30  
  Purchase #3 $216.39   8.456%   $234.6879   $234.69   $234.70   $234.70  
  Purchase #4 $51.36   6.154%   $54.5207   $54.52   $54.50   $54.50  
  Purchase #5 $30.72   6.353%   $32.6716   $32.67   $32.65   $32.70  
  Purchase #6 $141.34   13.348%   $160.2061   $160.21   $160.20   $160.20  
  Purchase #7 $199.83   7.855%   $215.5266   $215.53   $215.55   $215.50  
  7 purchase totals = $951.45       $1,023.7420   $1,023.75   $1,023.70   $1,023.80