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 $97.65   6.191%   $103.6955   $103.70   $103.70   $103.70  
  Purchase #2 $53.97   5.416%   $56.893   $56.89   $56.90   $56.90  
  Purchase #3 $45.62   10.161%   $50.2554   $50.26   $50.25   $50.30  
  Purchase #4 $212.90   5.736%   $225.1119   $225.11   $225.10   $225.10  
  Purchase #5 $186.91   12.461%   $210.2009   $210.20   $210.20   $210.20  
  Purchase #6 $34.64   3.204%   $35.7499   $35.75   $35.75   $35.70  
  Purchase #7 $203.59   11.314%   $226.6242   $226.62   $226.60   $226.60  
  7 purchase totals = $835.28       $908.5308   $908.53   $908.50   $908.50