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 $59.83   13.568%   $67.9477   $67.95   $67.95   $67.90  
  Purchase #2 $118.95   13.200%   $134.6514   $134.65   $134.65   $134.70  
  Purchase #3 $182.64   13.346%   $207.0151   $207.02   $207.00   $207.00  
  Purchase #4 $246.39   10.821%   $273.0519   $273.05   $273.05   $273.10  
  Purchase #5 $52.50   10.210%   $57.8603   $57.86   $57.85   $57.90  
  Purchase #6 $26.49   8.119%   $28.6407   $28.64   $28.65   $28.60  
  Purchase #7 $62.59   5.685%   $66.1482   $66.15   $66.15   $66.10  
  7 purchase totals = $749.39       $835.3153   $835.32   $835.30   $835.30