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 $204.37   8.482%   $221.7047   $221.70   $221.70   $221.70  
  Purchase #2 $56.46   6.496%   $60.1276   $60.13   $60.15   $60.10  
  Purchase #3 $195.59   6.493%   $208.2897   $208.29   $208.30   $208.30  
  Purchase #4 $146.63   13.250%   $166.0585   $166.06   $166.05   $166.10  
  Purchase #5 $133.27   9.108%   $145.4082   $145.41   $145.40   $145.40  
  Purchase #6 $60.27   12.216%   $67.6326   $67.63   $67.65   $67.60  
  Purchase #7 $58.59   13.288%   $66.3754   $66.38   $66.40   $66.40  
  7 purchase totals = $855.18       $935.5967   $935.60   $935.65   $935.60