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 $211.57   11.332%   $235.5451   $235.55   $235.55   $235.50  
  Purchase #2 $38.57   11.455%   $42.9882   $42.99   $43.00   $43.00  
  Purchase #3 $113.55   3.558%   $117.5901   $117.59   $117.60   $117.60  
  Purchase #4 $144.25   9.347%   $157.733   $157.73   $157.75   $157.70  
  Purchase #5 $246.55   6.586%   $262.7878   $262.79   $262.80   $262.80  
  Purchase #6 $24.78   11.284%   $27.5762   $27.58   $27.60   $27.60  
  Purchase #7 $165.64   5.647%   $174.9937   $174.99   $175.00   $175.00  
  7 purchase totals = $944.91       $1,019.2141   $1,019.22   $1,019.30   $1,019.20