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 $52.51   9.591%   $57.5462   $57.55   $57.55   $57.50  
  Purchase #2 $241.52   11.395%   $269.0412   $269.04   $269.05   $269.00  
  Purchase #3 $183.63   4.294%   $191.5151   $191.52   $191.50   $191.50  
  Purchase #4 $56.92   10.751%   $63.0395   $63.04   $63.05   $63.00  
  Purchase #5 $14.80   13.175%   $16.7499   $16.75   $16.75   $16.70  
  Purchase #6 $227.88   13.176%   $257.9055   $257.91   $257.90   $257.90  
  Purchase #7 $97.97   12.323%   $110.0428   $110.04   $110.05   $110.00  
  7 purchase totals = $875.23       $965.8402   $965.85   $965.85   $965.60