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 $58.87   11.823%   $65.8302   $65.83   $65.85   $65.80  
  Purchase #2 $213.47   10.405%   $235.6816   $235.68   $235.70   $235.70  
  Purchase #3 $79.75   9.622%   $87.4235   $87.42   $87.40   $87.40  
  Purchase #4 $13.66   12.118%   $15.3153   $15.32   $15.30   $15.30  
  Purchase #5 $181.86   6.326%   $193.3645   $193.36   $193.35   $193.40  
  Purchase #6 $196.46   5.736%   $207.7289   $207.73   $207.75   $207.70  
  Purchase #7 $221.74   7.248%   $237.8117   $237.81   $237.80   $237.80  
  7 purchase totals = $965.81       $1,043.1557   $1,043.15   $1,043.15   $1,043.10