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 $166.46   6.126%   $176.6573   $176.66   $176.65   $176.70  
  Purchase #2 $141.78   6.729%   $151.3204   $151.32   $151.30   $151.30  
  Purchase #3 $154.56   6.156%   $164.0747   $164.07   $164.05   $164.10  
  Purchase #4 $135.95   9.332%   $148.6369   $148.64   $148.65   $148.60  
  Purchase #5 $120.49   6.196%   $127.9556   $127.96   $127.95   $128.00  
  Purchase #6 $101.46   10.524%   $112.1377   $112.14   $112.15   $112.10  
  Purchase #7 $68.96   9.154%   $75.2726   $75.27   $75.25   $75.30  
  7 purchase totals = $889.66       $956.0552   $956.06   $956.00   $956.10