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 $109.57   9.153%   $119.5989   $119.60   $119.60   $119.60  
  Purchase #2 $144.95   4.819%   $151.9351   $151.94   $151.95   $151.90  
  Purchase #3 $116.27   11.554%   $129.7038   $129.70   $129.70   $129.70  
  Purchase #4 $169.57   11.346%   $188.8094   $188.81   $188.80   $188.80  
  Purchase #5 $112.54   8.477%   $122.08   $122.08   $122.10   $122.10  
  Purchase #6 $238.43   4.217%   $248.4846   $248.48   $248.50   $248.50  
  Purchase #7 $70.96   9.743%   $77.8736   $77.87   $77.85   $77.90  
  7 purchase totals = $962.29       $1,038.4854   $1,038.48   $1,038.50   $1,038.50