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 $106.87   11.190%   $118.8288   $118.83   $118.85   $118.80  
  Purchase #2 $197.29   8.226%   $213.5191   $213.52   $213.50   $213.50  
  Purchase #3 $52.57   11.480%   $58.605   $58.61   $58.60   $58.60  
  Purchase #4 $207.39   4.706%   $217.1498   $217.15   $217.15   $217.10  
  Purchase #5 $246.70   12.120%   $276.6   $276.60   $276.60   $276.60  
  Purchase #6 $210.86   9.320%   $230.5122   $230.51   $230.50   $230.50  
  Purchase #7 $107.25   3.449%   $110.9491   $110.95   $110.95   $110.90  
  7 purchase totals = $1,128.93       $1,226.1640   $1,226.17   $1,226.15   $1,226.00