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 $68.78   6.724%   $73.4048   $73.40   $73.40   $73.40  
  Purchase #2 $228.44   7.845%   $246.3611   $246.36   $246.35   $246.40  
  Purchase #3 $70.53   9.722%   $77.3869   $77.39   $77.40   $77.40  
  Purchase #4 $28.66   11.404%   $31.9284   $31.93   $31.95   $31.90  
  Purchase #5 $69.80   10.400%   $77.0592   $77.06   $77.05   $77.10  
  Purchase #6 $202.92   7.260%   $217.652   $217.65   $217.65   $217.70  
  Purchase #7 $43.82   9.719%   $48.0789   $48.08   $48.10   $48.10  
  7 purchase totals = $712.95       $771.8713   $771.87   $771.90   $772.00