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 $102.29   12.152%   $114.7203   $114.72   $114.70   $114.70  
  Purchase #2 $59.44   9.654%   $65.1783   $65.18   $65.20   $65.20  
  Purchase #3 $97.35   13.822%   $110.8057   $110.81   $110.80   $110.80  
  Purchase #4 $101.51   12.408%   $114.1054   $114.11   $114.10   $114.10  
  Purchase #5 $186.25   3.462%   $192.698   $192.70   $192.70   $192.70  
  Purchase #6 $236.49   12.754%   $266.6519   $266.65   $266.65   $266.70  
  Purchase #7 $141.51   12.405%   $159.0643   $159.06   $159.05   $159.10  
  7 purchase totals = $924.84       $1,023.2239   $1,023.23   $1,023.20   $1,023.30