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 $193.87   5.787%   $205.0893   $205.09   $205.10   $205.10  
  Purchase #2 $85.81   12.701%   $96.7087   $96.71   $96.70   $96.70  
  Purchase #3 $95.51   13.269%   $108.1832   $108.18   $108.20   $108.20  
  Purchase #4 $246.43   9.523%   $269.8975   $269.90   $269.90   $269.90  
  Purchase #5 $11.60   12.580%   $13.0593   $13.06   $13.05   $13.10  
  Purchase #6 $125.74   7.663%   $135.3755   $135.38   $135.40   $135.40  
  Purchase #7 $112.29   9.283%   $122.7139   $122.71   $122.70   $122.70  
  7 purchase totals = $871.25       $951.0274   $951.03   $951.05   $951.10