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 $194.38   6.316%   $206.657   $206.66   $206.65   $206.70  
  Purchase #2 $111.89   12.104%   $125.4332   $125.43   $125.45   $125.40  
  Purchase #3 $76.58   8.417%   $83.0257   $83.03   $83.05   $83.00  
  Purchase #4 $188.69   6.844%   $201.6039   $201.60   $201.60   $201.60  
  Purchase #5 $119.61   6.298%   $127.143   $127.14   $127.15   $127.10  
  Purchase #6 $188.91   10.667%   $209.061   $209.06   $209.05   $209.10  
  Purchase #7 $218.46   12.164%   $245.0335   $245.03   $245.05   $245.00  
  7 purchase totals = $1,098.52       $1,197.9573   $1,197.95   $1,198.00   $1,197.90