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 $56.70   11.192%   $63.0459   $63.05   $63.05   $63.00  
  Purchase #2 $98.71   4.206%   $102.8617   $102.86   $102.85   $102.90  
  Purchase #3 $235.44   13.319%   $266.7983   $266.80   $266.80   $266.80  
  Purchase #4 $20.58   3.512%   $21.3028   $21.30   $21.30   $21.30  
  Purchase #5 $183.34   9.230%   $200.2623   $200.26   $200.25   $200.30  
  Purchase #6 $161.84   4.855%   $169.6973   $169.70   $169.70   $169.70  
  Purchase #7 $34.58   5.860%   $36.6064   $36.61   $36.60   $36.60  
  7 purchase totals = $791.19       $860.5747   $860.58   $860.55   $860.60