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 $183.53   13.758%   $208.7801   $208.78   $208.80   $208.80  
  Purchase #2 $145.45   5.633%   $153.6432   $153.64   $153.65   $153.60  
  Purchase #3 $102.88   12.126%   $115.3552   $115.36   $115.35   $115.40  
  Purchase #4 $191.88   12.801%   $216.4426   $216.44   $216.45   $216.40  
  Purchase #5 $40.81   10.133%   $44.9453   $44.95   $44.95   $44.90  
  Purchase #6 $213.64   13.647%   $242.7955   $242.80   $242.80   $242.80  
  Purchase #7 $38.52   13.352%   $43.6632   $43.66   $43.65   $43.70  
  7 purchase totals = $916.71       $1,025.6251   $1,025.63   $1,025.65   $1,025.60