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 $212.94   3.506%   $220.4057   $220.41   $220.40   $220.40  
  Purchase #2 $117.43   8.856%   $127.8296   $127.83   $127.85   $127.80  
  Purchase #3 $163.36   8.408%   $177.0953   $177.10   $177.10   $177.10  
  Purchase #4 $246.96   3.621%   $255.9024   $255.90   $255.90   $255.90  
  Purchase #5 $192.98   6.478%   $205.4812   $205.48   $205.50   $205.50  
  Purchase #6 $233.54   8.122%   $252.5081   $252.51   $252.50   $252.50  
  Purchase #7 $106.60   13.826%   $121.3385   $121.34   $121.35   $121.30  
  7 purchase totals = $1,273.81       $1,360.5608   $1,360.57   $1,360.60   $1,360.50