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 $179.95   8.366%   $195.0046   $195.00   $195.00   $195.00  
  Purchase #2 $239.97   5.851%   $254.0106   $254.01   $254.00   $254.00  
  Purchase #3 $11.88   7.443%   $12.7642   $12.76   $12.75   $12.80  
  Purchase #4 $187.31   8.498%   $203.2276   $203.23   $203.25   $203.20  
  Purchase #5 $141.66   8.371%   $153.5184   $153.52   $153.50   $153.50  
  Purchase #6 $78.85   12.451%   $88.6676   $88.67   $88.65   $88.70  
  Purchase #7 $248.38   7.612%   $267.2867   $267.29   $267.30   $267.30  
  7 purchase totals = $1,088.00       $1,174.4797   $1,174.48   $1,174.45   $1,174.50