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 $60.80   12.783%   $68.5721   $68.57   $68.55   $68.60  
  Purchase #2 $201.67   6.786%   $215.3553   $215.36   $215.35   $215.40  
  Purchase #3 $248.71   6.615%   $265.1622   $265.16   $265.15   $265.20  
  Purchase #4 $191.55   3.166%   $197.6145   $197.61   $197.60   $197.60  
  Purchase #5 $230.93   3.245%   $238.4237   $238.42   $238.40   $238.40  
  Purchase #6 $161.79   12.375%   $181.8115   $181.81   $181.80   $181.80  
  Purchase #7 $11.38   11.206%   $12.6552   $12.66   $12.65   $12.70  
  7 purchase totals = $1,106.83       $1,179.5945   $1,179.59   $1,179.50   $1,179.70