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 $59.56   10.228%   $65.6518   $65.65   $65.65   $65.70  
  Purchase #2 $17.54   8.695%   $19.0651   $19.07   $19.05   $19.10  
  Purchase #3 $137.68   10.604%   $152.2796   $152.28   $152.30   $152.30  
  Purchase #4 $226.75   8.866%   $246.8537   $246.85   $246.85   $246.90  
  Purchase #5 $73.93   9.239%   $80.7604   $80.76   $80.75   $80.80  
  Purchase #6 $48.47   12.533%   $54.5447   $54.54   $54.55   $54.50  
  Purchase #7 $197.78   4.184%   $206.0551   $206.06   $206.05   $206.10  
  7 purchase totals = $761.71       $825.2104   $825.21   $825.20   $825.40