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 $181.79   10.730%   $201.2961   $201.30   $201.30   $201.30  
  Purchase #2 $39.42   5.466%   $41.5747   $41.57   $41.55   $41.60  
  Purchase #3 $35.31   8.623%   $38.3548   $38.35   $38.35   $38.40  
  Purchase #4 $224.86   6.635%   $239.7795   $239.78   $239.80   $239.80  
  Purchase #5 $30.59   12.660%   $34.4627   $34.46   $34.45   $34.50  
  Purchase #6 $140.42   11.311%   $156.3029   $156.30   $156.30   $156.30  
  Purchase #7 $38.49   8.232%   $41.6585   $41.66   $41.65   $41.70  
  7 purchase totals = $690.88       $753.4292   $753.42   $753.40   $753.60