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 $49.73   3.808%   $51.6237   $51.62   $51.60   $51.60  
  Purchase #2 $210.83   11.693%   $235.4824   $235.48   $235.50   $235.50  
  Purchase #3 $88.78   3.138%   $91.5659   $91.57   $91.55   $91.60  
  Purchase #4 $49.31   10.616%   $54.5447   $54.54   $54.55   $54.50  
  Purchase #5 $67.67   4.358%   $70.6191   $70.62   $70.60   $70.60  
  Purchase #6 $218.30   4.593%   $228.3265   $228.33   $228.35   $228.30  
  Purchase #7 $241.62   5.187%   $254.1528   $254.15   $254.15   $254.20  
  7 purchase totals = $926.24       $986.3151   $986.31   $986.30   $986.30