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 $154.56   5.816%   $163.5492   $163.55   $163.55   $163.50  
  Purchase #2 $121.84   9.496%   $133.4099   $133.41   $133.40   $133.40  
  Purchase #3 $95.50   12.763%   $107.6887   $107.69   $107.70   $107.70  
  Purchase #4 $171.55   5.641%   $181.2271   $181.23   $181.25   $181.20  
  Purchase #5 $95.38   8.143%   $103.1468   $103.15   $103.15   $103.10  
  Purchase #6 $65.47   4.720%   $68.5602   $68.56   $68.55   $68.60  
  Purchase #7 $176.75   8.555%   $191.871   $191.87   $191.85   $191.90  
  7 purchase totals = $881.05       $949.4529   $949.46   $949.45   $949.40