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 $145.66   10.308%   $160.6746   $160.67   $160.65   $160.70  
  Purchase #2 $215.71   3.280%   $222.7853   $222.79   $222.80   $222.80  
  Purchase #3 $95.95   12.283%   $107.7355   $107.74   $107.75   $107.70  
  Purchase #4 $66.48   10.226%   $73.2782   $73.28   $73.30   $73.30  
  Purchase #5 $206.66   9.371%   $226.0261   $226.03   $226.05   $226.00  
  Purchase #6 $44.92   5.245%   $47.2761   $47.28   $47.30   $47.30  
  Purchase #7 $175.88   5.776%   $186.0388   $186.04   $186.05   $186.00  
  7 purchase totals = $951.26       $1,023.8146   $1,023.83   $1,023.90   $1,023.80