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 $153.58   11.828%   $171.7454   $171.75   $171.75   $171.70  
  Purchase #2 $176.87   12.464%   $198.9151   $198.92   $198.90   $198.90  
  Purchase #3 $103.63   13.605%   $117.7289   $117.73   $117.75   $117.70  
  Purchase #4 $54.99   4.431%   $57.4266   $57.43   $57.45   $57.40  
  Purchase #5 $110.45   10.402%   $121.939   $121.94   $121.95   $121.90  
  Purchase #6 $102.49   5.682%   $108.3135   $108.31   $108.30   $108.30  
  Purchase #7 $177.57   7.874%   $191.5519   $191.55   $191.55   $191.60  
  7 purchase totals = $879.58       $967.6204   $967.63   $967.65   $967.50