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 $106.76   11.710%   $119.2616   $119.26   $119.25   $119.30  
  Purchase #2 $219.91   6.709%   $234.6638   $234.66   $234.65   $234.70  
  Purchase #3 $54.25   6.568%   $57.8131   $57.81   $57.80   $57.80  
  Purchase #4 $115.65   11.187%   $128.5878   $128.59   $128.60   $128.60  
  Purchase #5 $131.94   5.490%   $139.1835   $139.18   $139.20   $139.20  
  Purchase #6 $213.47   12.662%   $240.4996   $240.50   $240.50   $240.50  
  Purchase #7 $217.95   5.841%   $230.6805   $230.68   $230.70   $230.70  
  7 purchase totals = $1,059.93       $1,150.6899   $1,150.68   $1,150.70   $1,150.80