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 $83.28   11.190%   $92.599   $92.60   $92.60   $92.60  
  Purchase #2 $97.35   10.679%   $107.746   $107.75   $107.75   $107.70  
  Purchase #3 $244.40   6.513%   $260.3178   $260.32   $260.30   $260.30  
  Purchase #4 $25.32   5.470%   $26.705   $26.71   $26.70   $26.70  
  Purchase #5 $126.85   9.609%   $139.039   $139.04   $139.05   $139.00  
  Purchase #6 $246.75   8.783%   $268.4221   $268.42   $268.40   $268.40  
  Purchase #7 $22.70   9.321%   $24.8159   $24.82   $24.80   $24.80  
  7 purchase totals = $846.65       $919.6448   $919.66   $919.60   $919.50