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 $117.40   6.278%   $124.7704   $124.77   $124.75   $124.80  
  Purchase #2 $184.79   8.749%   $200.9573   $200.96   $200.95   $201.00  
  Purchase #3 $69.48   7.795%   $74.896   $74.90   $74.90   $74.90  
  Purchase #4 $219.99   11.544%   $245.3856   $245.39   $245.40   $245.40  
  Purchase #5 $191.85   3.421%   $198.4132   $198.41   $198.40   $198.40  
  Purchase #6 $76.38   9.816%   $83.8775   $83.88   $83.90   $83.90  
  Purchase #7 $126.66   7.828%   $136.5749   $136.57   $136.55   $136.60  
  7 purchase totals = $986.55       $1,064.8749   $1,064.88   $1,064.85   $1,065.00