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 $60.42   5.488%   $63.7358   $63.74   $63.75   $63.70  
  Purchase #2 $122.76   3.266%   $126.7693   $126.77   $126.75   $126.80  
  Purchase #3 $99.37   3.261%   $102.6105   $102.61   $102.60   $102.60  
  Purchase #4 $160.89   9.230%   $175.7401   $175.74   $175.75   $175.70  
  Purchase #5 $188.76   9.279%   $206.275   $206.28   $206.30   $206.30  
  Purchase #6 $139.30   3.809%   $144.6059   $144.61   $144.60   $144.60  
  Purchase #7 $165.69   11.174%   $184.2042   $184.20   $184.20   $184.20  
  7 purchase totals = $937.19       $1,003.9408   $1,003.95   $1,003.95   $1,003.90