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 $116.86   12.643%   $131.6346   $131.63   $131.65   $131.60  
  Purchase #2 $52.78   4.169%   $54.9804   $54.98   $55.00   $55.00  
  Purchase #3 $104.78   9.150%   $114.3674   $114.37   $114.35   $114.40  
  Purchase #4 $123.44   9.255%   $134.8644   $134.86   $134.85   $134.90  
  Purchase #5 $165.93   4.267%   $173.0102   $173.01   $173.00   $173.00  
  Purchase #6 $227.49   7.279%   $244.049   $244.05   $244.05   $244.00  
  Purchase #7 $128.75   10.317%   $142.0331   $142.03   $142.05   $142.00  
  7 purchase totals = $920.03       $994.9391   $994.93   $994.95   $994.90