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 $132.68   10.806%   $147.0174   $147.02   $147.00   $147.00  
  Purchase #2 $206.62   12.752%   $232.9682   $232.97   $232.95   $233.00  
  Purchase #3 $23.50   6.731%   $25.0818   $25.08   $25.10   $25.10  
  Purchase #4 $64.35   6.261%   $68.379   $68.38   $68.40   $68.40  
  Purchase #5 $98.62   5.702%   $104.2433   $104.24   $104.25   $104.20  
  Purchase #6 $239.83   4.348%   $250.2578   $250.26   $250.25   $250.30  
  Purchase #7 $250.41   4.459%   $261.5758   $261.58   $261.60   $261.60  
  7 purchase totals = $1,016.01       $1,089.5233   $1,089.53   $1,089.55   $1,089.60