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 $203.78   5.447%   $214.8799   $214.88   $214.90   $214.90  
  Purchase #2 $14.59   5.115%   $15.3363   $15.34   $15.35   $15.30  
  Purchase #3 $75.67   4.682%   $79.2129   $79.21   $79.20   $79.20  
  Purchase #4 $35.32   5.151%   $37.1393   $37.14   $37.15   $37.10  
  Purchase #5 $184.45   9.846%   $202.6109   $202.61   $202.60   $202.60  
  Purchase #6 $63.45   11.390%   $70.677   $70.68   $70.70   $70.70  
  Purchase #7 $134.94   11.235%   $150.1005   $150.10   $150.10   $150.10  
  7 purchase totals = $712.20       $769.9568   $769.96   $770.00   $769.90