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 $64.51   7.836%   $69.565   $69.57   $69.55   $69.60  
  Purchase #2 $91.32   4.797%   $95.7006   $95.70   $95.70   $95.70  
  Purchase #3 $11.95   8.246%   $12.9354   $12.94   $12.95   $12.90  
  Purchase #4 $238.72   12.264%   $267.9966   $268.00   $268.00   $268.00  
  Purchase #5 $92.65   11.105%   $102.9388   $102.94   $102.95   $102.90  
  Purchase #6 $242.74   5.107%   $255.1367   $255.14   $255.15   $255.10  
  Purchase #7 $185.40   5.749%   $196.0586   $196.06   $196.05   $196.10  
  7 purchase totals = $927.29       $1,000.3317   $1,000.35   $1,000.35   $1,000.30