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 $228.57   6.871%   $244.275   $244.28   $244.30   $244.30  
  Purchase #2 $214.99   9.760%   $235.973   $235.97   $235.95   $236.00  
  Purchase #3 $105.28   9.644%   $115.4332   $115.43   $115.45   $115.40  
  Purchase #4 $68.72   11.424%   $76.5706   $76.57   $76.55   $76.60  
  Purchase #5 $155.50   9.345%   $170.0315   $170.03   $170.05   $170.00  
  Purchase #6 $86.91   7.759%   $93.6533   $93.65   $93.65   $93.70  
  Purchase #7 $244.97   13.650%   $278.4084   $278.41   $278.40   $278.40  
  7 purchase totals = $1,104.94       $1,214.3450   $1,214.34   $1,214.35   $1,214.40