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 $55.30   11.824%   $61.8387   $61.84   $61.85   $61.80  
  Purchase #2 $14.55   3.849%   $15.11   $15.11   $15.10   $15.10  
  Purchase #3 $8.41   11.757%   $9.3988   $9.40   $9.40   $9.40  
  Purchase #4 $87.57   10.783%   $97.0127   $97.01   $97.00   $97.00  
  Purchase #5 $32.49   7.777%   $35.0167   $35.02   $35.00   $35.00  
  Purchase #6 $118.87   6.481%   $126.574   $126.57   $126.55   $126.60  
  Purchase #7 $38.88   3.125%   $40.095   $40.10   $40.10   $40.10  
  7 purchase totals = $356.07       $385.0459   $385.05   $385.00   $385.00