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 $67.35   12.855%   $76.0078   $76.01   $76.00   $76.00  
  Purchase #2 $57.77   6.786%   $61.6903   $61.69   $61.70   $61.70  
  Purchase #3 $236.48   3.751%   $245.3504   $245.35   $245.35   $245.40  
  Purchase #4 $139.55   4.459%   $145.7725   $145.77   $145.75   $145.80  
  Purchase #5 $91.68   3.529%   $94.9154   $94.92   $94.90   $94.90  
  Purchase #6 $244.50   11.764%   $273.263   $273.26   $273.25   $273.30  
  Purchase #7 $113.75   6.200%   $120.8025   $120.80   $120.80   $120.80  
  7 purchase totals = $951.08       $1,017.8019   $1,017.80   $1,017.75   $1,017.90