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 $17.62   8.180%   $19.0613   $19.06   $19.05   $19.10  
  Purchase #2 $105.80   12.261%   $118.7721   $118.77   $118.75   $118.80  
  Purchase #3 $156.52   12.606%   $176.2509   $176.25   $176.25   $176.30  
  Purchase #4 $200.81   6.443%   $213.7482   $213.75   $213.75   $213.70  
  Purchase #5 $111.66   8.336%   $120.968   $120.97   $120.95   $121.00  
  Purchase #6 $70.36   9.480%   $77.0301   $77.03   $77.05   $77.00  
  Purchase #7 $26.73   13.221%   $30.264   $30.26   $30.25   $30.30  
  7 purchase totals = $689.50       $756.0946   $756.09   $756.05   $756.20