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 $80.96   6.765%   $86.4369   $86.44   $86.45   $86.40  
  Purchase #2 $241.81   12.396%   $271.7848   $271.78   $271.80   $271.80  
  Purchase #3 $94.77   13.373%   $107.4436   $107.44   $107.45   $107.40  
  Purchase #4 $54.58   6.260%   $57.9967   $58.00   $58.00   $58.00  
  Purchase #5 $37.85   10.482%   $41.8174   $41.82   $41.80   $41.80  
  Purchase #6 $215.30   5.686%   $227.542   $227.54   $227.55   $227.50  
  Purchase #7 $214.39   7.107%   $229.6267   $229.63   $229.65   $229.60  
  7 purchase totals = $939.66       $1,022.6481   $1,022.65   $1,022.70   $1,022.50