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 $241.61   10.389%   $266.7109   $266.71   $266.70   $266.70  
  Purchase #2 $116.75   11.313%   $129.9579   $129.96   $129.95   $130.00  
  Purchase #3 $232.30   4.103%   $241.8313   $241.83   $241.85   $241.80  
  Purchase #4 $24.63   5.701%   $26.0342   $26.03   $26.05   $26.00  
  Purchase #5 $205.75   11.340%   $229.0821   $229.08   $229.10   $229.10  
  Purchase #6 $139.53   6.309%   $148.3329   $148.33   $148.35   $148.30  
  Purchase #7 $124.49   11.201%   $138.4341   $138.43   $138.45   $138.40  
  7 purchase totals = $1,085.06       $1,180.3834   $1,180.37   $1,180.45   $1,180.30