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 $54.72   8.241%   $59.2295   $59.23   $59.25   $59.20  
  Purchase #2 $192.87   8.760%   $209.7654   $209.77   $209.75   $209.80  
  Purchase #3 $155.85   6.720%   $166.3231   $166.32   $166.30   $166.30  
  Purchase #4 $232.65   12.190%   $261.01   $261.01   $261.00   $261.00  
  Purchase #5 $216.44   3.131%   $223.2167   $223.22   $223.20   $223.20  
  Purchase #6 $213.87   5.520%   $225.6756   $225.68   $225.70   $225.70  
  Purchase #7 $121.29   13.629%   $137.8206   $137.82   $137.80   $137.80  
  7 purchase totals = $1,187.69       $1,283.0409   $1,283.05   $1,283.00   $1,283.00