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 $85.30   9.693%   $93.5681   $93.57   $93.55   $93.60  
  Purchase #2 $115.29   9.293%   $126.0039   $126.00   $126.00   $126.00  
  Purchase #3 $127.52   8.718%   $138.6372   $138.64   $138.65   $138.60  
  Purchase #4 $93.28   10.297%   $102.885   $102.89   $102.90   $102.90  
  Purchase #5 $68.70   5.684%   $72.6049   $72.60   $72.60   $72.60  
  Purchase #6 $239.27   10.774%   $265.0489   $265.05   $265.05   $265.00  
  Purchase #7 $142.97   13.516%   $162.2938   $162.29   $162.30   $162.30  
  7 purchase totals = $872.33       $961.0418   $961.04   $961.05   $961.00