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 $153.52   3.368%   $158.6906   $158.69   $158.70   $158.70  
  Purchase #2 $11.28   8.248%   $12.2104   $12.21   $12.20   $12.20  
  Purchase #3 $77.92   3.561%   $80.6947   $80.69   $80.70   $80.70  
  Purchase #4 $90.87   7.600%   $97.7761   $97.78   $97.80   $97.80  
  Purchase #5 $168.43   8.247%   $182.3204   $182.32   $182.30   $182.30  
  Purchase #6 $106.84   3.396%   $110.4683   $110.47   $110.45   $110.50  
  Purchase #7 $193.56   3.305%   $199.9572   $199.96   $199.95   $200.00  
  7 purchase totals = $802.42       $842.1177   $842.12   $842.10   $842.20