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 $79.95   5.402%   $84.2689   $84.27   $84.25   $84.30  
  Purchase #2 $91.84   8.264%   $99.4297   $99.43   $99.45   $99.40  
  Purchase #3 $53.65   4.497%   $56.0626   $56.06   $56.05   $56.10  
  Purchase #4 $167.41   6.371%   $178.0757   $178.08   $178.10   $178.10  
  Purchase #5 $163.82   13.591%   $186.0848   $186.08   $186.10   $186.10  
  Purchase #6 $94.40   6.232%   $100.283   $100.28   $100.30   $100.30  
  Purchase #7 $25.43   13.264%   $28.803   $28.80   $28.80   $28.80  
  7 purchase totals = $676.50       $733.0077   $733.00   $733.05   $733.10