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 $158.97   10.601%   $175.8224   $175.82   $175.80   $175.80  
  Purchase #2 $180.36   5.861%   $190.9309   $190.93   $190.95   $190.90  
  Purchase #3 $41.32   6.849%   $44.15   $44.15   $44.15   $44.20  
  Purchase #4 $239.26   11.344%   $266.4017   $266.40   $266.40   $266.40  
  Purchase #5 $191.47   5.223%   $201.4705   $201.47   $201.45   $201.50  
  Purchase #6 $127.85   8.860%   $139.1775   $139.18   $139.20   $139.20  
  Purchase #7 $235.76   12.251%   $264.643   $264.64   $264.65   $264.60  
  7 purchase totals = $1,174.99       $1,282.5960   $1,282.59   $1,282.60   $1,282.60