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 $53.97   13.426%   $61.216   $61.22   $61.20   $61.20  
  Purchase #2 $24.89   6.688%   $26.5546   $26.55   $26.55   $26.60  
  Purchase #3 $83.56   13.317%   $94.6877   $94.69   $94.70   $94.70  
  Purchase #4 $78.60   8.269%   $85.0994   $85.10   $85.10   $85.10  
  Purchase #5 $9.65   9.121%   $10.5302   $10.53   $10.55   $10.50  
  Purchase #6 $186.50   5.837%   $197.386   $197.39   $197.40   $197.40  
  Purchase #7 $76.28   10.173%   $84.04   $84.04   $84.05   $84.00  
  7 purchase totals = $513.45       $559.5139   $559.52   $559.55   $559.50