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 $226.63   6.332%   $240.9802   $240.98   $241.00   $241.00  
  Purchase #2 $247.68   5.179%   $260.5073   $260.51   $260.50   $260.50  
  Purchase #3 $91.58   6.748%   $97.7598   $97.76   $97.75   $97.80  
  Purchase #4 $205.67   6.525%   $219.09   $219.09   $219.10   $219.10  
  Purchase #5 $49.61   7.286%   $53.2246   $53.22   $53.20   $53.20  
  Purchase #6 $30.47   3.293%   $31.4734   $31.47   $31.45   $31.50  
  Purchase #7 $247.67   5.197%   $260.5414   $260.54   $260.55   $260.50  
  7 purchase totals = $1,099.31       $1,163.5767   $1,163.57   $1,163.55   $1,163.60