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 $56.42   5.753%   $59.6658   $59.67   $59.65   $59.70  
  Purchase #2 $15.93   12.591%   $17.9357   $17.94   $17.95   $17.90  
  Purchase #3 $92.28   13.358%   $104.6068   $104.61   $104.60   $104.60  
  Purchase #4 $82.66   6.325%   $87.8882   $87.89   $87.90   $87.90  
  Purchase #5 $73.81   3.135%   $76.1239   $76.12   $76.10   $76.10  
  Purchase #6 $49.46   8.132%   $53.4821   $53.48   $53.50   $53.50  
  Purchase #7 $205.88   12.190%   $230.9768   $230.98   $231.00   $231.00  
  7 purchase totals = $576.44       $630.6793   $630.69   $630.70   $630.70