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 $247.65   10.780%   $274.3467   $274.35   $274.35   $274.30  
  Purchase #2 $132.54   10.682%   $146.6979   $146.70   $146.70   $146.70  
  Purchase #3 $176.88   13.663%   $201.0471   $201.05   $201.05   $201.00  
  Purchase #4 $69.41   3.461%   $71.8123   $71.81   $71.80   $71.80  
  Purchase #5 $100.94   13.533%   $114.6002   $114.60   $114.60   $114.60  
  Purchase #6 $214.69   10.300%   $236.8031   $236.80   $236.80   $236.80  
  Purchase #7 $62.35   5.352%   $65.687   $65.69   $65.70   $65.70  
  7 purchase totals = $1,004.46       $1,110.9943   $1,111.00   $1,111.00   $1,110.90