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 $201.77   10.814%   $223.5894   $223.59   $223.60   $223.60  
  Purchase #2 $167.76   12.475%   $188.6881   $188.69   $188.70   $188.70  
  Purchase #3 $175.68   4.675%   $183.893   $183.89   $183.90   $183.90  
  Purchase #4 $59.53   5.837%   $63.0048   $63.00   $63.00   $63.00  
  Purchase #5 $145.34   4.840%   $152.3745   $152.37   $152.35   $152.40  
  Purchase #6 $214.60   12.715%   $241.8864   $241.89   $241.90   $241.90  
  Purchase #7 $173.77   13.824%   $197.792   $197.79   $197.80   $197.80  
  7 purchase totals = $1,138.45       $1,251.2282   $1,251.22   $1,251.25   $1,251.30