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 $55.84   8.156%   $60.3943   $60.39   $60.40   $60.40  
  Purchase #2 $200.44   11.252%   $222.9935   $222.99   $223.00   $223.00  
  Purchase #3 $116.95   3.463%   $121   $121.00   $121.00   $121.00  
  Purchase #4 $44.93   8.752%   $48.8623   $48.86   $48.85   $48.90  
  Purchase #5 $198.63   7.751%   $214.0258   $214.03   $214.05   $214.00  
  Purchase #6 $244.66   5.487%   $258.0845   $258.08   $258.10   $258.10  
  Purchase #7 $134.94   3.175%   $139.2243   $139.22   $139.20   $139.20  
  7 purchase totals = $996.39       $1,064.5847   $1,064.57   $1,064.60   $1,064.60