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 $55.41   13.620%   $62.9568   $62.96   $62.95   $63.00  
  Purchase #2 $217.52   9.860%   $238.9675   $238.97   $238.95   $239.00  
  Purchase #3 $127.46   6.369%   $135.5779   $135.58   $135.60   $135.60  
  Purchase #4 $174.92   4.352%   $182.5325   $182.53   $182.55   $182.50  
  Purchase #5 $124.57   5.112%   $130.938   $130.94   $130.95   $130.90  
  Purchase #6 $151.84   5.113%   $159.6036   $159.60   $159.60   $159.60  
  Purchase #7 $112.84   10.365%   $124.5359   $124.54   $124.55   $124.50  
  7 purchase totals = $964.56       $1,035.1122   $1,035.12   $1,035.15   $1,035.10