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 $68.81   3.159%   $70.9837   $70.98   $71.00   $71.00  
  Purchase #2 $203.32   8.127%   $219.8438   $219.84   $219.85   $219.80  
  Purchase #3 $65.80   5.866%   $69.6598   $69.66   $69.65   $69.70  
  Purchase #4 $83.58   8.477%   $90.6651   $90.67   $90.65   $90.70  
  Purchase #5 $48.90   5.557%   $51.6174   $51.62   $51.60   $51.60  
  Purchase #6 $108.85   11.335%   $121.1881   $121.19   $121.20   $121.20  
  Purchase #7 $121.91   8.852%   $132.7015   $132.70   $132.70   $132.70  
  7 purchase totals = $701.17       $756.6594   $756.66   $756.65   $756.70