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 $234.61   11.117%   $260.6916   $260.69   $260.70   $260.70  
  Purchase #2 $154.27   3.520%   $159.7003   $159.70   $159.70   $159.70  
  Purchase #3 $58.70   9.103%   $64.0435   $64.04   $64.05   $64.00  
  Purchase #4 $201.36   11.676%   $224.8708   $224.87   $224.85   $224.90  
  Purchase #5 $53.63   8.661%   $58.2749   $58.27   $58.25   $58.30  
  Purchase #6 $122.70   10.393%   $135.4522   $135.45   $135.45   $135.50  
  Purchase #7 $177.96   7.360%   $191.0579   $191.06   $191.05   $191.10  
  7 purchase totals = $1,003.23       $1,094.0912   $1,094.08   $1,094.05   $1,094.20