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 $193.50   13.701%   $220.0114   $220.01   $220.00   $220.00  
  Purchase #2 $24.79   7.112%   $26.5531   $26.55   $26.55   $26.60  
  Purchase #3 $214.74   6.288%   $228.2429   $228.24   $228.25   $228.20  
  Purchase #4 $99.71   3.775%   $103.4741   $103.47   $103.45   $103.50  
  Purchase #5 $162.99   3.787%   $169.1624   $169.16   $169.15   $169.20  
  Purchase #6 $47.26   13.314%   $53.5522   $53.55   $53.55   $53.60  
  Purchase #7 $168.98   3.328%   $174.6037   $174.60   $174.60   $174.60  
  7 purchase totals = $911.97       $975.5998   $975.58   $975.55   $975.70