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 $217.65   10.239%   $239.9352   $239.94   $239.95   $239.90  
  Purchase #2 $83.47   11.149%   $92.7761   $92.78   $92.80   $92.80  
  Purchase #3 $243.69   10.659%   $269.6649   $269.66   $269.65   $269.70  
  Purchase #4 $101.77   11.799%   $113.7778   $113.78   $113.80   $113.80  
  Purchase #5 $219.37   4.327%   $228.8621   $228.86   $228.85   $228.90  
  Purchase #6 $152.36   7.298%   $163.4792   $163.48   $163.50   $163.50  
  Purchase #7 $183.72   5.814%   $194.4015   $194.40   $194.40   $194.40  
  7 purchase totals = $1,202.03       $1,302.8968   $1,302.90   $1,302.95   $1,303.00