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 $217.81   9.108%   $237.6481   $237.65   $237.65   $237.60  
  Purchase #2 $247.67   6.605%   $264.0286   $264.03   $264.05   $264.00  
  Purchase #3 $67.77   3.320%   $70.02   $70.02   $70.00   $70.00  
  Purchase #4 $87.68   11.747%   $97.9798   $97.98   $98.00   $98.00  
  Purchase #5 $202.97   5.612%   $214.3607   $214.36   $214.35   $214.40  
  Purchase #6 $6.95   8.261%   $7.5241   $7.52   $7.50   $7.50  
  Purchase #7 $30.68   7.737%   $33.0537   $33.05   $33.05   $33.10  
  7 purchase totals = $861.53       $924.6150   $924.61   $924.60   $924.60