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 $45.89   8.347%   $49.7204   $49.72   $49.70   $49.70  
  Purchase #2 $173.54   12.292%   $194.8715   $194.87   $194.85   $194.90  
  Purchase #3 $245.92   8.493%   $266.806   $266.81   $266.80   $266.80  
  Purchase #4 $116.54   6.863%   $124.5381   $124.54   $124.55   $124.50  
  Purchase #5 $236.30   9.190%   $258.016   $258.02   $258.00   $258.00  
  Purchase #6 $167.73   9.679%   $183.9646   $183.96   $183.95   $184.00  
  Purchase #7 $119.47   3.458%   $123.6013   $123.60   $123.60   $123.60  
  7 purchase totals = $1,105.39       $1,201.5179   $1,201.52   $1,201.45   $1,201.50