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 $173.66   6.384%   $184.7465   $184.75   $184.75   $184.70  
  Purchase #2 $91.93   11.225%   $102.2491   $102.25   $102.25   $102.20  
  Purchase #3 $195.63   3.104%   $201.7024   $201.70   $201.70   $201.70  
  Purchase #4 $180.78   4.236%   $188.4378   $188.44   $188.45   $188.40  
  Purchase #5 $17.39   7.682%   $18.7259   $18.73   $18.75   $18.70  
  Purchase #6 $221.27   13.728%   $251.6459   $251.65   $251.65   $251.60  
  Purchase #7 $61.64   9.743%   $67.6456   $67.65   $67.65   $67.60  
  7 purchase totals = $942.30       $1,015.1532   $1,015.17   $1,015.20   $1,014.90