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 $226.59   11.326%   $252.2536   $252.25   $252.25   $252.30  
  Purchase #2 $87.36   13.771%   $99.3903   $99.39   $99.40   $99.40  
  Purchase #3 $192.77   11.471%   $214.8826   $214.88   $214.90   $214.90  
  Purchase #4 $37.31   11.235%   $41.5018   $41.50   $41.50   $41.50  
  Purchase #5 $113.79   11.637%   $127.0317   $127.03   $127.05   $127.00  
  Purchase #6 $132.47   10.327%   $146.1502   $146.15   $146.15   $146.20  
  Purchase #7 $182.95   10.165%   $201.5469   $201.55   $201.55   $201.50  
  7 purchase totals = $973.24       $1,082.7571   $1,082.75   $1,082.80   $1,082.80