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 $177.91   13.704%   $202.2908   $202.29   $202.30   $202.30  
  Purchase #2 $210.96   11.297%   $234.7922   $234.79   $234.80   $234.80  
  Purchase #3 $52.96   3.439%   $54.7813   $54.78   $54.80   $54.80  
  Purchase #4 $191.58   7.612%   $206.1631   $206.16   $206.15   $206.20  
  Purchase #5 $200.85   13.247%   $227.4566   $227.46   $227.45   $227.50  
  Purchase #6 $230.78   6.676%   $246.1869   $246.19   $246.20   $246.20  
  Purchase #7 $30.58   12.621%   $34.4395   $34.44   $34.45   $34.40  
  7 purchase totals = $1,095.62       $1,206.1104   $1,206.11   $1,206.15   $1,206.20