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 $65.83   11.563%   $73.4419   $73.44   $73.45   $73.40  
  Purchase #2 $89.59   5.339%   $94.3732   $94.37   $94.35   $94.40  
  Purchase #3 $55.99   8.574%   $60.7906   $60.79   $60.80   $60.80  
  Purchase #4 $181.39   9.851%   $199.2587   $199.26   $199.25   $199.30  
  Purchase #5 $210.59   9.453%   $230.4971   $230.50   $230.50   $230.50  
  Purchase #6 $50.84   5.723%   $53.7496   $53.75   $53.75   $53.70  
  Purchase #7 $165.51   8.806%   $180.0848   $180.08   $180.10   $180.10  
  7 purchase totals = $819.74       $892.1959   $892.19   $892.20   $892.20