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 $59.79   9.774%   $65.6339   $65.63   $65.65   $65.60  
  Purchase #2 $47.77   11.160%   $53.1011   $53.10   $53.10   $53.10  
  Purchase #3 $99.70   10.715%   $110.3829   $110.38   $110.40   $110.40  
  Purchase #4 $225.64   9.370%   $246.7825   $246.78   $246.80   $246.80  
  Purchase #5 $122.35   5.563%   $129.1563   $129.16   $129.15   $129.20  
  Purchase #6 $13.48   11.736%   $15.062   $15.06   $15.05   $15.10  
  Purchase #7 $218.30   6.371%   $232.2079   $232.21   $232.20   $232.20  
  7 purchase totals = $787.03       $852.3266   $852.32   $852.35   $852.40