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 $22.80   13.827%   $25.9526   $25.95   $25.95   $26.00  
  Purchase #2 $208.93   8.385%   $226.4488   $226.45   $226.45   $226.40  
  Purchase #3 $165.72   5.197%   $174.3325   $174.33   $174.35   $174.30  
  Purchase #4 $35.87   5.683%   $37.9085   $37.91   $37.90   $37.90  
  Purchase #5 $121.45   11.116%   $134.9504   $134.95   $134.95   $135.00  
  Purchase #6 $102.70   7.676%   $110.5833   $110.58   $110.60   $110.60  
  Purchase #7 $203.59   9.384%   $222.6949   $222.69   $222.70   $222.70  
  7 purchase totals = $861.06       $932.8710   $932.86   $932.90   $932.90