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 $170.31   5.729%   $180.0671   $180.07   $180.05   $180.10  
  Purchase #2 $9.80   13.810%   $11.1534   $11.15   $11.15   $11.20  
  Purchase #3 $77.40   8.350%   $83.8629   $83.86   $83.85   $83.90  
  Purchase #4 $94.25   11.822%   $105.3922   $105.39   $105.40   $105.40  
  Purchase #5 $102.74   7.858%   $110.8133   $110.81   $110.80   $110.80  
  Purchase #6 $135.45   5.110%   $142.3715   $142.37   $142.35   $142.40  
  Purchase #7 $111.33   13.721%   $126.6056   $126.61   $126.60   $126.60  
  7 purchase totals = $701.28       $760.2660   $760.26   $760.20   $760.40