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 $48.87   13.714%   $55.572   $55.57   $55.55   $55.60  
  Purchase #2 $248.69   6.421%   $264.6584   $264.66   $264.65   $264.70  
  Purchase #3 $198.59   12.191%   $222.8001   $222.80   $222.80   $222.80  
  Purchase #4 $116.42   11.598%   $129.9224   $129.92   $129.90   $129.90  
  Purchase #5 $191.97   6.475%   $204.4001   $204.40   $204.40   $204.40  
  Purchase #6 $66.87   5.814%   $70.7578   $70.76   $70.75   $70.80  
  Purchase #7 $69.99   7.514%   $75.249   $75.25   $75.25   $75.20  
  7 purchase totals = $941.40       $1,023.3598   $1,023.36   $1,023.30   $1,023.40