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 $239.94   8.659%   $260.7164   $260.72   $260.70   $260.70  
  Purchase #2 $154.93   3.651%   $160.5865   $160.59   $160.60   $160.60  
  Purchase #3 $46.93   8.127%   $50.744   $50.74   $50.75   $50.70  
  Purchase #4 $47.25   11.463%   $52.6663   $52.67   $52.65   $52.70  
  Purchase #5 $117.69   7.782%   $126.8486   $126.85   $126.85   $126.80  
  Purchase #6 $198.39   4.840%   $207.9921   $207.99   $208.00   $208.00  
  Purchase #7 $133.88   10.625%   $148.1048   $148.10   $148.10   $148.10  
  7 purchase totals = $939.01       $1,007.6587   $1,007.66   $1,007.65   $1,007.60