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 $212.39   13.744%   $241.5809   $241.58   $241.60   $241.60  
  Purchase #2 $228.95   6.705%   $244.3011   $244.30   $244.30   $244.30  
  Purchase #3 $142.95   8.641%   $155.3023   $155.30   $155.30   $155.30  
  Purchase #4 $123.77   6.572%   $131.9042   $131.90   $131.90   $131.90  
  Purchase #5 $68.69   10.562%   $75.945   $75.95   $75.95   $75.90  
  Purchase #6 $79.73   4.814%   $83.5682   $83.57   $83.55   $83.60  
  Purchase #7 $30.83   13.253%   $34.9159   $34.92   $34.90   $34.90  
  7 purchase totals = $887.31       $967.5176   $967.52   $967.50   $967.50