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 $67.88   11.815%   $75.9   $75.90   $75.90   $75.90  
  Purchase #2 $237.28   6.554%   $252.8313   $252.83   $252.85   $252.80  
  Purchase #3 $126.47   11.248%   $140.6953   $140.70   $140.70   $140.70  
  Purchase #4 $24.36   10.163%   $26.8357   $26.84   $26.85   $26.80  
  Purchase #5 $166.86   11.774%   $186.5061   $186.51   $186.50   $186.50  
  Purchase #6 $81.81   6.516%   $87.1407   $87.14   $87.15   $87.10  
  Purchase #7 $13.52   8.638%   $14.6879   $14.69   $14.70   $14.70  
  7 purchase totals = $718.18       $784.5970   $784.61   $784.65   $784.50