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 $204.96   10.683%   $226.8559   $226.86   $226.85   $226.90  
  Purchase #2 $8.37   3.404%   $8.6549   $8.65   $8.65   $8.70  
  Purchase #3 $247.80   13.822%   $282.0509   $282.05   $282.05   $282.10  
  Purchase #4 $222.37   5.575%   $234.7671   $234.77   $234.75   $234.80  
  Purchase #5 $22.85   12.170%   $25.6308   $25.63   $25.65   $25.60  
  Purchase #6 $129.95   12.591%   $146.312   $146.31   $146.30   $146.30  
  Purchase #7 $114.76   10.109%   $126.3611   $126.36   $126.35   $126.40  
  7 purchase totals = $951.06       $1,050.6327   $1,050.63   $1,050.60   $1,050.80