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 $54.79   6.137%   $58.1525   $58.15   $58.15   $58.20  
  Purchase #2 $68.87   12.668%   $77.5945   $77.59   $77.60   $77.60  
  Purchase #3 $8.59   11.145%   $9.5474   $9.55   $9.55   $9.50  
  Purchase #4 $245.30   10.709%   $271.5692   $271.57   $271.55   $271.60  
  Purchase #5 $156.76   13.475%   $177.8834   $177.88   $177.90   $177.90  
  Purchase #6 $246.72   8.402%   $267.4494   $267.45   $267.45   $267.40  
  Purchase #7 $126.37   13.646%   $143.6145   $143.61   $143.60   $143.60  
  7 purchase totals = $907.40       $1,005.8109   $1,005.80   $1,005.80   $1,005.80