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 $59.92   4.578%   $62.6631   $62.66   $62.65   $62.70  
  Purchase #2 $157.81   10.393%   $174.2112   $174.21   $174.20   $174.20  
  Purchase #3 $72.72   13.211%   $82.327   $82.33   $82.35   $82.30  
  Purchase #4 $31.92   7.286%   $34.2457   $34.25   $34.25   $34.20  
  Purchase #5 $224.33   13.701%   $255.0655   $255.07   $255.05   $255.10  
  Purchase #6 $26.99   6.488%   $28.7411   $28.74   $28.75   $28.70  
  Purchase #7 $174.86   8.426%   $189.5937   $189.59   $189.60   $189.60  
  7 purchase totals = $748.55       $826.8473   $826.85   $826.85   $826.80