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 $8.43   7.786%   $9.0864   $9.09   $9.10   $9.10  
  Purchase #2 $8.98   10.869%   $9.956   $9.96   $9.95   $10.00  
  Purchase #3 $67.99   5.399%   $71.6608   $71.66   $71.65   $71.70  
  Purchase #4 $124.61   11.170%   $138.5289   $138.53   $138.55   $138.50  
  Purchase #5 $226.66   11.680%   $253.1339   $253.13   $253.15   $253.10  
  Purchase #6 $114.48   5.635%   $120.9309   $120.93   $120.95   $120.90  
  Purchase #7 $65.35   4.340%   $68.1862   $68.19   $68.20   $68.20  
  7 purchase totals = $616.50       $671.4831   $671.49   $671.55   $671.50