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 $239.52   10.557%   $264.8061   $264.81   $264.80   $264.80  
  Purchase #2 $216.86   13.178%   $245.4378   $245.44   $245.45   $245.40  
  Purchase #3 $160.59   6.858%   $171.6033   $171.60   $171.60   $171.60  
  Purchase #4 $8.26   11.831%   $9.2372   $9.24   $9.25   $9.20  
  Purchase #5 $95.30   13.582%   $108.2436   $108.24   $108.25   $108.20  
  Purchase #6 $16.94   3.399%   $17.5158   $17.52   $17.50   $17.50  
  Purchase #7 $194.83   3.579%   $201.803   $201.80   $201.80   $201.80  
  7 purchase totals = $932.30       $1,018.6468   $1,018.65   $1,018.65   $1,018.50