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 $187.25   11.612%   $208.9935   $208.99   $209.00   $209.00  
  Purchase #2 $221.35   7.810%   $238.6374   $238.64   $238.65   $238.60  
  Purchase #3 $40.45   3.620%   $41.9143   $41.91   $41.90   $41.90  
  Purchase #4 $193.92   10.825%   $214.9118   $214.91   $214.90   $214.90  
  Purchase #5 $204.67   8.683%   $222.4415   $222.44   $222.45   $222.40  
  Purchase #6 $181.41   11.230%   $201.7823   $201.78   $201.80   $201.80  
  Purchase #7 $234.67   4.642%   $245.5634   $245.56   $245.55   $245.60  
  7 purchase totals = $1,263.72       $1,374.2442   $1,374.23   $1,374.25   $1,374.20