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 $173.52   12.778%   $195.6924   $195.69   $195.70   $195.70  
  Purchase #2 $105.82   11.158%   $117.6274   $117.63   $117.65   $117.60  
  Purchase #3 $235.77   9.149%   $257.3406   $257.34   $257.35   $257.30  
  Purchase #4 $81.70   13.257%   $92.531   $92.53   $92.55   $92.50  
  Purchase #5 $151.69   6.327%   $161.2874   $161.29   $161.30   $161.30  
  Purchase #6 $169.45   5.508%   $178.7833   $178.78   $178.80   $178.80  
  Purchase #7 $210.46   11.807%   $235.309   $235.31   $235.30   $235.30  
  7 purchase totals = $1,128.41       $1,238.5711   $1,238.57   $1,238.65   $1,238.50