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 $241.82   10.438%   $267.0612   $267.06   $267.05   $267.10  
  Purchase #2 $27.54   5.524%   $29.0613   $29.06   $29.05   $29.10  
  Purchase #3 $19.95   5.687%   $21.0846   $21.08   $21.10   $21.10  
  Purchase #4 $102.59   9.310%   $112.1411   $112.14   $112.15   $112.10  
  Purchase #5 $77.74   12.729%   $87.6355   $87.64   $87.65   $87.60  
  Purchase #6 $222.45   3.267%   $229.7174   $229.72   $229.70   $229.70  
  Purchase #7 $127.32   5.838%   $134.7529   $134.75   $134.75   $134.80  
  7 purchase totals = $819.41       $881.4540   $881.45   $881.45   $881.50