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 $181.66   5.502%   $191.6549   $191.65   $191.65   $191.70  
  Purchase #2 $247.60   12.595%   $278.7852   $278.79   $278.80   $278.80  
  Purchase #3 $186.25   11.357%   $207.4024   $207.40   $207.40   $207.40  
  Purchase #4 $37.90   8.610%   $41.1632   $41.16   $41.15   $41.20  
  Purchase #5 $18.64   6.212%   $19.7979   $19.80   $19.80   $19.80  
  Purchase #6 $214.84   8.254%   $232.5729   $232.57   $232.55   $232.60  
  Purchase #7 $46.45   13.785%   $52.8531   $52.85   $52.85   $52.90  
  7 purchase totals = $933.34       $1,024.2296   $1,024.22   $1,024.20   $1,024.40