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 $62.63   6.413%   $66.6465   $66.65   $66.65   $66.60  
  Purchase #2 $105.67   3.712%   $109.5925   $109.59   $109.60   $109.60  
  Purchase #3 $186.32   8.638%   $202.4143   $202.41   $202.40   $202.40  
  Purchase #4 $79.25   3.740%   $82.214   $82.21   $82.20   $82.20  
  Purchase #5 $152.59   9.362%   $166.8755   $166.88   $166.90   $166.90  
  Purchase #6 $223.66   8.659%   $243.0267   $243.03   $243.05   $243.00  
  Purchase #7 $142.55   11.168%   $158.47   $158.47   $158.45   $158.50  
  7 purchase totals = $952.67       $1,029.2395   $1,029.24   $1,029.25   $1,029.20