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 $118.91   12.847%   $134.1864   $134.19   $134.20   $134.20  
  Purchase #2 $246.39   8.535%   $267.4194   $267.42   $267.40   $267.40  
  Purchase #3 $73.60   7.813%   $79.3504   $79.35   $79.35   $79.40  
  Purchase #4 $87.35   7.678%   $94.0567   $94.06   $94.05   $94.10  
  Purchase #5 $128.95   13.612%   $146.5027   $146.50   $146.50   $146.50  
  Purchase #6 $196.43   5.222%   $206.6876   $206.69   $206.70   $206.70  
  Purchase #7 $115.44   7.751%   $124.3878   $124.39   $124.40   $124.40  
  7 purchase totals = $967.07       $1,052.5910   $1,052.60   $1,052.60   $1,052.70