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 $130.28   3.151%   $134.3851   $134.39   $134.40   $134.40  
  Purchase #2 $183.39   6.641%   $195.5689   $195.57   $195.55   $195.60  
  Purchase #3 $48.55   7.219%   $52.0548   $52.05   $52.05   $52.10  
  Purchase #4 $43.67   6.225%   $46.3885   $46.39   $46.40   $46.40  
  Purchase #5 $168.86   5.201%   $177.6424   $177.64   $177.65   $177.60  
  Purchase #6 $114.73   7.708%   $123.5734   $123.57   $123.55   $123.60  
  Purchase #7 $71.93   4.270%   $75.0014   $75.00   $75.00   $75.00  
  7 purchase totals = $761.41       $804.6145   $804.61   $804.60   $804.70