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 $161.76   10.435%   $178.6397   $178.64   $178.65   $178.60  
  Purchase #2 $230.27   11.701%   $257.2139   $257.21   $257.20   $257.20  
  Purchase #3 $32.70   11.122%   $36.3369   $36.34   $36.35   $36.30  
  Purchase #4 $151.31   13.699%   $172.038   $172.04   $172.05   $172.00  
  Purchase #5 $76.95   3.720%   $79.8125   $79.81   $79.80   $79.80  
  Purchase #6 $16.91   3.391%   $17.4834   $17.48   $17.50   $17.50  
  Purchase #7 $250.90   8.814%   $273.0143   $273.01   $273.00   $273.00  
  7 purchase totals = $920.80       $1,014.5387   $1,014.53   $1,014.55   $1,014.40