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 $113.25   10.245%   $124.8525   $124.85   $124.85   $124.90  
  Purchase #2 $212.91   6.481%   $226.7087   $226.71   $226.70   $226.70  
  Purchase #3 $94.86   8.518%   $102.9402   $102.94   $102.95   $102.90  
  Purchase #4 $163.60   9.300%   $178.8148   $178.81   $178.80   $178.80  
  Purchase #5 $246.55   12.269%   $276.7992   $276.80   $276.80   $276.80  
  Purchase #6 $247.89   8.801%   $269.7068   $269.71   $269.70   $269.70  
  Purchase #7 $60.60   12.573%   $68.2192   $68.22   $68.20   $68.20  
  7 purchase totals = $1,139.66       $1,248.0414   $1,248.04   $1,248.00   $1,248.00