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 $181.41   6.738%   $193.6334   $193.63   $193.65   $193.60  
  Purchase #2 $247.94   11.598%   $276.6961   $276.70   $276.70   $276.70  
  Purchase #3 $16.28   5.459%   $17.1687   $17.17   $17.15   $17.20  
  Purchase #4 $131.61   7.199%   $141.0846   $141.08   $141.10   $141.10  
  Purchase #5 $85.57   8.642%   $92.965   $92.97   $92.95   $93.00  
  Purchase #6 $52.65   9.103%   $57.4427   $57.44   $57.45   $57.40  
  Purchase #7 $222.89   6.273%   $236.8719   $236.87   $236.85   $236.90  
  7 purchase totals = $938.35       $1,015.8624   $1,015.86   $1,015.85   $1,015.90