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 $246.83   5.688%   $260.8697   $260.87   $260.85   $260.90  
  Purchase #2 $114.89   5.543%   $121.2584   $121.26   $121.25   $121.30  
  Purchase #3 $150.92   9.545%   $165.3253   $165.33   $165.35   $165.30  
  Purchase #4 $122.89   3.811%   $127.5733   $127.57   $127.55   $127.60  
  Purchase #5 $56.77   3.769%   $58.9097   $58.91   $58.90   $58.90  
  Purchase #6 $106.42   8.755%   $115.7371   $115.74   $115.75   $115.70  
  Purchase #7 $154.37   5.659%   $163.1058   $163.11   $163.10   $163.10  
  7 purchase totals = $953.09       $1,012.7793   $1,012.79   $1,012.75   $1,012.80