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 $134.89   8.162%   $145.8997   $145.90   $145.90   $145.90  
  Purchase #2 $67.58   9.450%   $73.9663   $73.97   $73.95   $74.00  
  Purchase #3 $80.82   12.874%   $91.2248   $91.22   $91.20   $91.20  
  Purchase #4 $175.66   12.443%   $197.5174   $197.52   $197.50   $197.50  
  Purchase #5 $164.59   12.631%   $185.3794   $185.38   $185.40   $185.40  
  Purchase #6 $93.41   3.553%   $96.7289   $96.73   $96.75   $96.70  
  Purchase #7 $131.63   3.147%   $135.7724   $135.77   $135.75   $135.80  
  7 purchase totals = $848.58       $926.4889   $926.49   $926.45   $926.50