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 $70.63   5.686%   $74.646   $74.65   $74.65   $74.60  
  Purchase #2 $250.35   8.263%   $271.0364   $271.04   $271.05   $271.00  
  Purchase #3 $83.66   8.125%   $90.4574   $90.46   $90.45   $90.50  
  Purchase #4 $217.64   11.174%   $241.9591   $241.96   $241.95   $242.00  
  Purchase #5 $37.92   9.808%   $41.6392   $41.64   $41.65   $41.60  
  Purchase #6 $179.62   5.210%   $188.9782   $188.98   $189.00   $189.00  
  Purchase #7 $115.64   4.851%   $121.2497   $121.25   $121.25   $121.20  
  7 purchase totals = $955.46       $1,029.9660   $1,029.98   $1,030.00   $1,029.90