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 $69.40   10.736%   $76.8508   $76.85   $76.85   $76.90  
  Purchase #2 $85.44   11.512%   $95.2759   $95.28   $95.30   $95.30  
  Purchase #3 $228.34   11.716%   $255.0923   $255.09   $255.10   $255.10  
  Purchase #4 $161.77   13.331%   $183.3356   $183.34   $183.35   $183.30  
  Purchase #5 $60.54   11.782%   $67.6728   $67.67   $67.65   $67.70  
  Purchase #6 $240.65   4.236%   $250.8439   $250.84   $250.85   $250.80  
  Purchase #7 $70.60   7.577%   $75.9494   $75.95   $75.95   $75.90  
  7 purchase totals = $916.74       $1,005.0207   $1,005.02   $1,005.05   $1,005.00