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 $60.96   13.514%   $69.1981   $69.20   $69.20   $69.20  
  Purchase #2 $116.67   6.563%   $124.3271   $124.33   $124.35   $124.30  
  Purchase #3 $128.95   7.637%   $138.7979   $138.80   $138.80   $138.80  
  Purchase #4 $96.57   13.280%   $109.3945   $109.39   $109.40   $109.40  
  Purchase #5 $52.86   6.686%   $56.3942   $56.39   $56.40   $56.40  
  Purchase #6 $135.87   10.800%   $150.544   $150.54   $150.55   $150.50  
  Purchase #7 $199.83   4.320%   $208.4627   $208.46   $208.45   $208.50  
  7 purchase totals = $791.71       $857.1185   $857.11   $857.15   $857.10