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 $111.41   6.413%   $118.5547   $118.55   $118.55   $118.60  
  Purchase #2 $220.83   8.567%   $239.7485   $239.75   $239.75   $239.70  
  Purchase #3 $10.33   11.746%   $11.5434   $11.54   $11.55   $11.50  
  Purchase #4 $216.45   4.564%   $226.3288   $226.33   $226.35   $226.30  
  Purchase #5 $184.72   12.729%   $208.233   $208.23   $208.25   $208.20  
  Purchase #6 $190.67   5.487%   $201.1321   $201.13   $201.15   $201.10  
  Purchase #7 $44.28   6.225%   $47.0364   $47.04   $47.05   $47.00  
  7 purchase totals = $978.69       $1,052.5769   $1,052.57   $1,052.65   $1,052.40