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 $241.75   12.464%   $271.8817   $271.88   $271.90   $271.90  
  Purchase #2 $177.71   11.697%   $198.4967   $198.50   $198.50   $198.50  
  Purchase #3 $38.97   5.476%   $41.104   $41.10   $41.10   $41.10  
  Purchase #4 $127.73   5.272%   $134.4639   $134.46   $134.45   $134.50  
  Purchase #5 $99.49   6.815%   $106.2702   $106.27   $106.25   $106.30  
  Purchase #6 $144.93   10.639%   $160.3491   $160.35   $160.35   $160.30  
  Purchase #7 $47.89   11.866%   $53.5726   $53.57   $53.55   $53.60  
  7 purchase totals = $878.47       $966.1382   $966.13   $966.10   $966.20