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 $59.44   6.112%   $63.073   $63.07   $63.05   $63.10  
  Purchase #2 $161.63   13.295%   $183.1187   $183.12   $183.10   $183.10  
  Purchase #3 $168.42   5.112%   $177.0296   $177.03   $177.05   $177.00  
  Purchase #4 $134.64   12.368%   $151.2923   $151.29   $151.30   $151.30  
  Purchase #5 $47.92   12.505%   $53.9124   $53.91   $53.90   $53.90  
  Purchase #6 $48.25   12.867%   $54.4583   $54.46   $54.45   $54.50  
  Purchase #7 $22.56   6.264%   $23.9732   $23.97   $23.95   $24.00  
  7 purchase totals = $642.86       $706.8575   $706.85   $706.80   $706.90