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 $54.57   9.739%   $59.8846   $59.88   $59.90   $59.90  
  Purchase #2 $172.32   11.682%   $192.4504   $192.45   $192.45   $192.50  
  Purchase #3 $170.45   8.663%   $185.2161   $185.22   $185.20   $185.20  
  Purchase #4 $86.75   9.628%   $95.1023   $95.10   $95.10   $95.10  
  Purchase #5 $95.83   6.132%   $101.7063   $101.71   $101.70   $101.70  
  Purchase #6 $138.53   7.792%   $149.3243   $149.32   $149.30   $149.30  
  Purchase #7 $157.99   11.634%   $176.3706   $176.37   $176.35   $176.40  
  7 purchase totals = $876.44       $960.0546   $960.05   $960.00   $960.10