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   11.213%   $63.0578   $63.06   $63.05   $63.10  
  Purchase #2 $154.47   6.821%   $165.0064   $165.01   $165.00   $165.00  
  Purchase #3 $110.61   8.757%   $120.2961   $120.30   $120.30   $120.30  
  Purchase #4 $6.30   10.268%   $6.9469   $6.95   $6.95   $6.90  
  Purchase #5 $50.42   10.325%   $55.6259   $55.63   $55.65   $55.60  
  Purchase #6 $193.40   10.556%   $213.8153   $213.82   $213.80   $213.80  
  Purchase #7 $202.39   12.784%   $228.2635   $228.26   $228.25   $228.30  
  7 purchase totals = $774.29       $853.0119   $853.03   $853.00   $853.00