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 $215.77   12.165%   $242.0184   $242.02   $242.00   $242.00  
  Purchase #2 $225.59   4.392%   $235.4979   $235.50   $235.50   $235.50  
  Purchase #3 $87.58   4.359%   $91.3976   $91.40   $91.40   $91.40  
  Purchase #4 $139.77   12.582%   $157.3559   $157.36   $157.35   $157.40  
  Purchase #5 $139.45   13.179%   $157.8281   $157.83   $157.85   $157.80  
  Purchase #6 $214.52   5.653%   $226.6468   $226.65   $226.65   $226.60  
  Purchase #7 $245.66   7.723%   $264.6323   $264.63   $264.65   $264.60  
  7 purchase totals = $1,268.34       $1,375.3770   $1,375.39   $1,375.40   $1,375.30