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 $182.28   11.824%   $203.8328   $203.83   $203.85   $203.80  
  Purchase #2 $71.58   4.294%   $74.6536   $74.65   $74.65   $74.70  
  Purchase #3 $188.43   4.735%   $197.3522   $197.35   $197.35   $197.40  
  Purchase #4 $26.32   4.217%   $27.4299   $27.43   $27.45   $27.40  
  Purchase #5 $142.84   6.421%   $152.0118   $152.01   $152.00   $152.00  
  Purchase #6 $66.38   4.538%   $69.3923   $69.39   $69.40   $69.40  
  Purchase #7 $10.46   13.458%   $11.8677   $11.87   $11.85   $11.90  
  7 purchase totals = $688.29       $736.5403   $736.53   $736.55   $736.60