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 $64.61   7.708%   $69.5901   $69.59   $69.60   $69.60  
  Purchase #2 $33.61   13.202%   $38.0472   $38.05   $38.05   $38.00  
  Purchase #3 $150.87   12.702%   $170.0335   $170.03   $170.05   $170.00  
  Purchase #4 $133.90   13.294%   $151.7007   $151.70   $151.70   $151.70  
  Purchase #5 $96.65   11.254%   $107.527   $107.53   $107.55   $107.50  
  Purchase #6 $44.43   12.156%   $49.8309   $49.83   $49.85   $49.80  
  Purchase #7 $95.96   10.264%   $105.8093   $105.81   $105.80   $105.80  
  7 purchase totals = $620.03       $692.5387   $692.54   $692.60   $692.40