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 $38.86   5.651%   $41.056   $41.06   $41.05   $41.10  
  Purchase #2 $209.87   12.299%   $235.6819   $235.68   $235.70   $235.70  
  Purchase #3 $236.30   5.784%   $249.9676   $249.97   $249.95   $250.00  
  Purchase #4 $41.38   3.224%   $42.7141   $42.71   $42.70   $42.70  
  Purchase #5 $105.87   13.593%   $120.2609   $120.26   $120.25   $120.30  
  Purchase #6 $141.28   7.601%   $152.0187   $152.02   $152.00   $152.00  
  Purchase #7 $200.48   11.471%   $223.4771   $223.48   $223.50   $223.50  
  7 purchase totals = $974.04       $1,065.1763   $1,065.18   $1,065.15   $1,065.30